Eneloop charger criteria

John Bentley · Oct 9, 2017

Intro

What criteria should we be using to regard an Eneloop charger as one that "works well"? In other words, what features would an eneloop charger need for it to not count as "flawed"?

I'd appreciate any help to answer that question (however we frame it). What follows is my current answer for you to criticize or otherwise respond to. I'd like to see if we could build a community consensus around this criteria.

I'll offer the following stipulation for ranking chargers in general:

"Flawed". The charger is able to charge the battery multiple times, perhaps even the number of times that the battery is rated for, but there is at least one flaw in the charger's design. A flaw, that is, that entails we'd eliminate it as a candidate to buy, if we were ideally informed buyers. Example flaws might be: no clear indication when full charge has been reached; a risk of early or late termination; or being unable to select a desired charging rate for all slots.
"Works Well". The charger is able to charge the battery multiple times, perhaps even the number of times that the battery is rated for, and there are no annoying flaws in the charger's design. A charger in this category is a candidate to buy, for an ideally informed buyer.
"Excellent". The charger "works well" and over and above that has a degree of polish, or some additional outstanding features, that make it highly desirable to buy, for an ideally informed buyer.

Having read this thread and read various charger reviews, to various levels of thoroughness, selecting a set of chargers that "works well" with eneloops, let alone is an "excellent" charger, remains elusive. The set of chargers listed in the first post appear to be able to charge eneloops. And evidently many people are using those chargers. But, so far in my research, they all seem "flawed".

I suspect this is not only because I'm new to batteries and chargers (at a depth of knowledge to start posting on a specialist forum like this one), and therefore have large holes in my current knowledge, but also because there appears to be a lack of consensus in this community around the necessary features for an eneloop charger that "works well".

If we can reach a consensus on what it takes for a charger to work well then we'll be in a better position to make specific recommendations in a thread like Eneloops: what charger do I need? (info and discussion thead). However, for the current thread I'd suggest mention of specific chargers be made only in so far as they bear on thinking about the criteria in general.

Can Eneloops be trickle charged?

The views of a few sources ...

Woodbank Communications. 2005. "Battery Chargers and Charging Methods." http://www.mpoweruk.com/chargers.htm.

NiMH cells on the other hand will be damaged by prolonged trickle charge.

AskMisterWizard.com. n.d. "The Dirty Little Secret about Nickle-Metal Hydride (NiMh) Batteries." http://askmisterwizard.com/Electricity/NiMhDirtyLittleSecret/NiMhPage01Full.htm.

Nickle-Metal Hydride batteries tend to remain cool while they are charging up. However, if a battery charger continues to supply charging energy after a full charge, all of that excess energy is turned to heat within the cell, and that heat can damage or destroy it.

On those sources it would seem best to use a charger that puts no charge into an Eneloop cell once it has reached full charge.

HKJ, provider of the most thorough and comprehensive reviews of chargers, has sometimes expressed a view consistent with the above ...

HKJ. n.d. "Charger Opus BT-C3100 V2.1." Accessed 2017. http://lygte-info.dk/review/Review Charger Opus BT-C3100 V2.1 UK.html.

Also note that the charger uses trickle charging when the main charge is finished, this is not really a good idea for LSD [Low self discharge, as Eneloops are] cells.

However, HKJ also expressed a willingness to use a trickle charge (although that seems to be as a last resort) ...

"Review of Charger SkyRC NC2500." Accessed 09 24, 2017. http://lygte-info.dk/review/Review Charger SkyRC NC2500 UK.html.

With NiMH batteries I will either use -dv/dt termination and no trickle charge or maximum voltage termination with 10mA trickle charge. There is no reason to use a higher trickle charge.

Many chargers will provide a low current charge to Eneloops after reaching some sort of termination point. And Eneloops seem to tolerate such a low current charge, as HKJ allows.

This is also consistent with my (very non scientific) experience. I've been using an MW6178 Intercept charger for perhaps 10 years that uses "trickle charging" - although I don't know at what current. Until recently it has been a reliable charger, despite the tickle charging (generally I remove the batteries as soon as the fast charge stops, with an alarm. But if I miss the alarm the batteries might trickle charge for at most a few hours).

Incidentally, at least one charger, the Powerex (Formerly Maha) MH-C9000, provides two low current charges after termination ...

The charger uses about 2 hours to charge the battery, then it terminates on voltage and uses another two hours to top the battery [at about 50 mA], before it switches to a trickle charge [0 < x < 10 mA ?]. The charger will report done after the first two hours [Soon after main charging]" http://lygte-info.dk/review/Review Charger Powerex MH-C9000 UK.html

In short, until better evidence can be brought to bear I'll conclude it's best NOT to trickle charge Eneloops (nor apply any other low level charge after termination, a "top off" charge), even though they can tolerate some trickle (or other low level) charging.

What charging rates should be used for eneloops in principle?

SilverFox, 08-26-2009, 08:42 AM, "Re: Appropriate Charge Rate for NiMH Batteries". http://www.candlepowerforums.com/vb...MH-Batteries&p=3062412&viewfull=1#post3062412

There is enough evidence to support charging in the 0.5 - 1.0C range that the battery manufacturers actually recommend it.

That charging range does seem supported by the single most important manufacturer when it comes to Eneloops: Panasonic. ....

Panasonic - Charge methods for Nickel Metal Hydride Batteries. 2005. "Charge methods for Nickel Metal Hydride Batteries." In Nickel Metal Hydride Handbook, 12-13. https://na.industrial.panasonic.com/sites/default/pidsa/files/downloads/files/panasonic_nimh_chargemethods.pdf.

Rapid charge current: 1CmA (rapid charge temperature range: 0°C to 40°). In order to exercise proper control to stop rapid charge, it is recommended that batteries be charged at over 0.5CmA but less than 1CmA. Charging batteries at a current in excess of 1CmA may cause the safety vent to be activated by a rise in the internal pressure of the batteries, thereby resulting in electrolyte leakage.

... "CmA". During charging and discharging, CmA is a value indicating current and expressed as a multiple of nominal capacity. Substitute "C" with the battery's nominal capacity when calculating. For example, for a 1500mAh battery of 0.033CmA, this value is equal to 1/30 x 1500, or roughly 50mA. [In other words "CmA" is used here where others commonly represent this with "C".]

The above 2005 documentation I've quoted nowhere mentions the brand name "Eneloop". This is because it wasn't until 2010 that Panasonic bought Sanyo. Sanyo was the inventor and original manufacturer of Eneloops.

Despite Panasonic's talk of "Nickel Metal Hydride Batteries" in general I'm relying on a defeasible assumption that this can be applied to the special category of Nickel Metal Hydride Batteries which are the low self-discharge Eneloops. In other words if anyone can find Eneloop specific documentation: that'd be a better source.

But in the absence of further evidence the recommended in principle charging rate for Eneloops seems to be 0.5 to 1.0C.

Is there a reason for preferring one end of that range over the other?

Well Panasonic stipulates 1.0C above.

That seems consistent with Silverfox's information and experiments (Silverfox could you verify that the following experiment was on a non-eneloop Nickel Metal Hydride chemistry?)

Every chemical engineer involved with testing has told me that overcharging kills NiMh chemistry, and the quickest way to overcharge is to use a charge rate below 0.5C. The preferred rate is 1C …

I set out to see if I could get 500 cycles from a set of batteries. I took 9 cells in a battery holder and ran a test. The cells were 2400 mAh capacity. I charged them at 2.5 amps and discharged them at 1.0 amps down to 1.0 volts per cell. Every 50 cycles, I ran a 16 hour balancing charge. The cells barely warmed up during charging. The charger never missed a termination because I had the charge quantity set to 2650 and the charger never terminated on quantity. At 653 cycles I terminated the test. The capacity had dropped below 80% of its initial capacity, and that is my criteria for termination.

I followed the manufacturers recommendation and charged at 1C. I got more than the advertised 500 cycles from my set of 9 cells. I think charging at 1C works well, and I highly recommend it.

.... The next project is to do the same thing with Eneloop cells.

... and that project would also be informative if a set of cells were charged at 0.5C versus a set charged at 1.0C.

However, in the absence of that data and despite the above expressions of preference for a charging rate of 1.0C ... if there's a risk of damage *above* 1.0C and a charger doesn't risk missing termination on a given lower charge ... one might be inclined to insert a safety margin *below* 1.0C.

For example HKJ, in the Review of the SkyRC NC2500, has a chart for a high capacity EneloopXX, at about 2600 mAh, that has been charged at only 1000 mA (search for the string "Using -dv/dt termination also works for eneloop XX"). That's a charging rate of about 0.4C.

HKJ was, of course, putting a charger through it's paces to see how it performs under extremes. I wouldn't draw the conclusion that HKJ recommends 0.4C as something to use in everyday practice. But HKJ's experiments show that at least some chargers can terminate even when charging below the recommended 0.5C rate (at least for the relatively new cells that HKJ generally, but not always, uses).

So my conclusion is that in principle, and in general, we'll want to charge somewhere between the recommended range 0.5 to 1.0C charging rate. And that there's no hard evidence for preferring one end of the range rather than the other. Within the recommended range, you should be OK.

What charging rates should be used in practice?

The following constitute the various models of Eneloops I currently possess:

Form Factor	Model	Name	Max Capacity (mAh)	Min Capacity (mAh)	Recommended Charging Lower Bound at 0.5C~	Recommended Charging Upper Bound at 1.0C~	Charging Rate in practice (mA)
AAA	BK-4MCCE	Eneloop 4th Gen	800	750	375	750	500
AA	HR-3UTG	Eneloop 1st Gen	2000	1900	950	1900	1500
AA	BK-3MCCE	Eneloop 4th Gen	2000	1900	950	1900	1500
AA	BK-3HCCE	Eneloop Pro	2550	2450	1225	2450	1500

On termination there is no charge.
~ Recommended Charging Range based on Min Capacity in order to be conservative at not exceeding 1.0C over the lifetime of the battery.

Of note is that I've recently acquired the higher capacity Eneloop Pros. A charging rate of 1000mA would fall below the recommended charging lower bound (0.5C = 1225ma).

Given that model range of Eneloops, which would not be uncommon among those who've been using Eneloops for some while, and to make life simple I've settled on only two "charging rates in practice" that correlate to a form factor: 500mA for AAA's and 1500mA for AA's.

Therefore a "works well" charger would need to:

Be able to charge at 500mA or 1500mA in all its slots; and, for convenience ...
Automatically select those charging rates based on form factor (whether it uses the physical dimensions or electrical properties of the inserted cells).

There wouldn't be a need to be discriminate against a charger that came, from the factory, with different default charging rates (e.g. 500mA and 1000mA). So long, that is, as one could change those defaults, rather than have to manually select the rate every time a battery was inserted.

Termination methods

There generally seems to be three termination methods for use with a NiMH battery:
1. Negative delta voltage (NDV or -dV/dt). That is, terminate when there is a relatively quick *drop* in voltage as the battery reach full capacity.
2. Temperature. That is, terminate when a temperature has been reached.
3. Timer. That is, terminate some time after charge start.

What happens after termination is a separate matter. A charger might: stop charging; apply a trickle charge; apply a "top off" charge; or apply a "top off" charge then a trickle charge.

When chargers make available, or rely upon, a "top off" charge then termination becomes ambiguous. One could regard "termination" at point at "top off" charge start, or "top off" charge end.

Often enough chargers seem able to use all three termination methods. And when they do they generally (inclusively) Or them together in the priority listed. That is, the first ambition is to terminate using -dV/dt. Failing that terminate on temperature. Failing that, terminate on a timer. In this way the last two termination methods serve as a backup for the first.

Most, if not all, of [HKJ's charger reviews](http://lygte-info.dk/info/roundCellChargerIndex UK.html) have charts that establish how the charger terminates, under various conditions.

In short, a basic requirement for a NiMH charger would entail that, at least for fresh batteries and for charging at the recommended rate (between 0.5 and 1.0C), it will consistently terminate using the negative delta voltage method; and that it has the other two termination methods as a backup.

Per Slot Display

I'd suggest a per slot display for a charger to "work well".

That is, a per slot display of the basic battery values: present capacity in mAh or as a percentage of full; charging rate in A or mA; and present voltage in volts. Pressing a button to cycle between those values wouldn't disqualify a charger, nor would pressing a button to provide further detail for a particular slot. But if we have to press a button to see *any* value for a slot (e.g. as with the Xtar Dragon VP4 Plus - requiring toggling between the inner and outer slots) ... that would count as a flaw.

Visual Termination Alarm

Some kind of "full" indication would seem to be essential. Whether that means the word "full" or "done" on a LCD display; and/or a light illuminates or changes colour.

Audible Termination Alarm

I'm quite surprised that audible alarms on termination are the exception and not the rule. An audible alarm becomes less critical if there is no charge after termination: your batteries aren't going to be unnecessarily degraded if you leave it in the charger. However, even where there is no charge after termination I'd suggest an audible alarm is valuable simply because you might want to use your batteries as soon as possible.

On the other hand, I have read of some who hate audible alarms. So whether a charger has an audible alarm might be more of a personal preference.

However, all personal preferences would be readily accommodated if a charger has an audible alarm that can be, through the settings, switched off (so it never goes off).

So I suggest a "works well" charger must have an audible alarm that can be configured to never go off.

Summary

I offer that an Eneloop (low self-discharge Nickel Metal Hydride (NiMH)) charger must have the following features in order to be regarded as "working well" and not "flawed":

Configurable to charge to 500 mA and 1500 mA, for AAA and AA eneloops respectively.
The charge rate configuration needs to be done only once (if at all) and from then on the charging rate is determined by form factor (whether via physical dimensions or electrical properties).
Terminates by negative delta voltage (NDV or -dV/dt), with termination by temperature, then timer, as backups.
Per slot display of the basic battery values: present capacity in mAh or as a percentage of full; charging rate in A or mA; present voltage in volts.
Visual termination alarm.
Audible termination alarm which can be toggled off through the settings.

What do you reckon?

Edit 2017-10-22: Formatting

hiuintahs · Oct 9, 2017

Wow, you've done some reading. Have you looked over this report?
http://www.candlepowerforums.com/vb/showthread.php?410902-Battery-charging-NiMH

I wonder if you are trying to turn NiMh charging into too much of a science project. (Not trying to be rude or anything, but just wondering if you're trying to find something that might not exist). There are a lot of good chargers out there and they are discussed on this forum. It's not really that critical. The NiMh is fairly forgiving. Basically the best chargers are those that utilize dV/dT, and the battery doesn't get too hot. Most of the issues that I have seen in HKJ's reports involve over charging and undercharging. In fact I think the issue at hand is just exactly where is the point that the battery is fully charged without over charging it (too much)? That's the question at hand in my opinion. HKJ comments on a variety of different methods.

If you can't find what you consider the perfect charger........that's when it's fun to design one's own charger. Post #14

.
http://www.candlepowerforums.com/vb...tteries-and-chargers-do-you-have-(photo-them)

ChrisGarrett · Oct 9, 2017

Holy wall of text Batman!

tl;dr

Here's to you and post two.

Chris

hiuintahs · Oct 9, 2017

Comments in red. After reading your final summary, I thought it was pretty good and thought I'd share what I do. (Not that its the best way though as I am still learning)

I offer that an Eneloop (low self-discharge Nickel Metal Hydride (NiMH)) charger must have the following features in order to be regarded as "working well" and not "flawed":

* On termination there is no charge. Once I reach dV/dT I let the charge run for another 5 minutes and call that good. At a lower charge level I may change my software to run a little longer. I do not trickle charge past that point though. I don't think that its harmful (as long as its a small trickle) if you do......just not sure how beneficial it really is. I just wouldn't rely on the trickle charge as a charging mechanism.
* Configurable to charge to 500 mA and 1500 mA, for AAA and AA eneloops respectively. I have 250mA, 500mA, and 1000mA as an option. 1500mA would be a nicety but if doing 4 bays at the same time it requires a larger power supply. So it becomes more a size factor as the decision rather than a dependability and reliability one from what I have seen. It doesn't seem to matter with the lower charge amounts other than it just takes longer to charge at the lower levels. The only risk is that the dV/dT is smaller and if your software and A/D resolution can't pick it up, then its a risk of over charging. In development, I once over charged a battery and the voltage simply will not climb above a certain point (say around 1.56v or thereabouts depending on the individual cell at hand) and what happens is all the charge energy just gets converted to heat.
* The charge rate configuration needs to be done only once (if at all) and from then on the charging rate is determined by form factor (whether via physical dimensions or electrical properties). That is hard to do especially if the charger also does Lithium Ion. Just one click of the operator can set the charge rate. I think that is good enough.
* Terminates by negative delta voltage (NDV or -dV/dt), with termination by temperature, then timer, as backups. Yes
* Per slot display of the basic battery values: present capacity in mAh or as a percentage of full; charging rate in A or mA; present voltage in volts. Yes, love displayed values. Displaying mAh requires more software to write. I have yet to do that, but that might be nice.
* Visual termination alarm. Definitely need something to tell you its done. Can be either an LED that blinks or info on an LCD display.
* Audible termination alarm which can be toggled off through the settings. I personally don't think an audible termination alarm is necessary unless this was a situation where batteries are constantly being charged. But yes if one is included it needs to able to be turned off.

What do you reckon?[/

iamlucky13 · Oct 9, 2017

You describe your final criteria as a "works well" charger, but it's more like the "as good as it gets" charger.

Even Sanyo themselves have been selling their batteries with dumb chargers that terminate after a set time regardless of the initial state of charge, and only charge in pairs. While I tend, like you, to think of this as a flawed method of charger, Sanyo is clearly not concerned with getting too many complaints about premature battery death using these chargers.

If you do want good life from your batteries, I think the critical features are individual cell control, -dV/dt termination, and time termination as a backup (or for fast chargers, temperature termination).

I'm not worried about a readout of voltage, although it can be nice to have. Fully charged voltage can vary between different brands of cells, and I think also between new and well-used cells. Readout of mAh capacity is very nice to have, but not critical. It may also be nice to have a recondition feature where the charger will automatically discharge and recharge a battery several times in a row, which in NiMH batteries usually improves capacity if it has declined over time.

Regarding trickle charging, of the two statements from HKJ you quoted, one is a charger with 10 mA of trickle charge current, which is pretty minimal, and one that looks from the graphs to be around 50 mA of trickle charge current. It makes sense to be more concerned about the latter case.

Regarding charge rate - rates above 0.5C are often recommended because the faster charger results in a more obvious -dV/dt signal. However, HKJ has tested even some like chargers like Panasonic BQ-CC17 as consistently properly terminating despite only charging at less than 0.2C. As far as I know, reliable termination is the second most significant reason for charge currents above 0.5C, after the convenience of faster charging.

However, if you're for some reason stuck using a dumb charger, it is instead important to charge slowly to avoid over-heating the battery during the inevitable over-charging.

Unless issues are documented that he missed, I'm willing to trust anything HKJ labels as a good charger, or gives two smiley faces to in his index, as "works well."

http://lygte-info.dk/info/roundCellChargerIndex UK.html

fmc1 · Oct 9, 2017

John

Nice job on your post, great read thank you. It is very informative and I know a lot of work went into it.

I have a small suggestion. You list three termination methods. I would add a fourth called voltage termination. Some chargers will charge a NiMH to a certain voltage like 1.50V and then just stop with no top off or trickle charge, I have two cheap eastshine chargers that do this. After the battery rests a while the voltage will settle in between 1.40v and 1.45V. Others do top offs based on time after voltage or sort or a hybrid of voltage and time.

Looking at your 7 bullet points for a "working well" charger. I can add that the skyrc mc3000 hits 6.5 but not all 7 because it can't tell the difference between AA's and AAA's without operator input. Since both regular eneloop AA and AAA charge programs on my mc3000's are assigned to one of the shortcuts, it's a one key operation to switch. I also use different programs for pros vs regular eneloops with pros having a higher charge current than regulars.

Thanks

Frank

John Bentley · Oct 21, 2017

Thanks all for the great responses.

Wall of text

@ChrisGarrett. For someone to write a post that counts as "a wall of text" is a serious foul in internet terms.

http://www.urbandictionary.com/define.php?term=wall of text

A piece of writing that does not use proper grammar and generally looks like a giant essay with 20 to 400 sentences without using paragraphs or any bit of spacing at all.

Given my extensive use of paragraphs, and spacing, I don't think my post can accurately described as a "wall of text". If there are any grammar errors, something I regularly fall prey to, I'd appreciate your identifying them.

If you just mean that the current formatting is a bit hard on the eyes then I agree. I was part way through formatting it when I inadvertently hit "post" rather than "preview". I apologise for this and I'll correct the formatting when I post a bit more and receive editing privileges.

If you mean my post was long, or overly long, then I suggest you use "long", or "overly long", as "wall of text" means something else.

Despite your claiming my post counted as a "wall of text", I take it your DiCaprio Cheers was sincere rather than sarcastic. So a sincere big DiCaprio Cheers back at you.

Termination Methods

@hiuintahs:

... just wondering if you're trying to find something that might not exist.

I wondered the same thing:

Having read this thread and read various charger reviews, to various levels of thoroughness, selecting a set of chargers that "works well" with eneloops, let alone is an "excellent" charger, remains elusive.

It was fantastic of you to point me towards HKJ's Battery charging NiMH. That clarifies a great deal about termination methods.

For present purposes I'll pick out two interesting things ...

dT/dt termination (Temperature raise). I have not seen any chargers using temperature termination, but usual [sic] it is a good indicator the battery is full

... It seems, however, that's since changed for the good. In HKJ's review of the SkyRC MC3000 (to choose an example) there is mention of ...

CAPACITY, CUT TIME and CUT TEMP are safety settings and can be used to terminate a charge on abnormal conditions.

@fmc1

I have a small suggestion. You list three termination methods. I would add a fourth called voltage termination.

Thanks. From HKJ's Battery charging NiMH I can see that termination method, and other funky methods, listed. Although it would probably better be called "Voltage point termination" ... termination when a voltage point is reached.

There's also listed there "0dv/dt termination", another method again and subtly different to Voltage point termination, as you allude to ("Others do top offs based on time after voltage or sort or a hybrid of voltage and time").

Charging Rates

HKJ concludes:

0.5A for AAA and 1A for AA is fine.

... but this appears to be in the context where the AA battery is about 2,000 mA rather than the higher capacity Eneloop Pros of about 2,500 mA.

If 0.5C to 1.0C charging is the golden rule, then my suggested 500mA for AAA's and 1500mA for AA's would seem to remain the right settings to aim for, if you had a set of Eneloops were like mine (which include Eneloop Pros). That would be consistent with HKJ's conclusion above (assuming we are both going off the golden rule).

hiuintahs (other issues)

hiuintahs:

In fact I think the issue at hand is just exactly where is the point that the battery is fully charged without over charging it (too much).

Yes that's critical.

Great to see your own designed and built charger, and accompanying explanation of what you get it to do.

I have 250mA, 500mA, and 1000mA as an option. 1500mA would be a nicety but if doing 4 bays at the same time it requires a larger power supply. So it becomes more a size factor.

But is having a larger power supply a problem at all (maybe in the context of using a 12V car charger?)?

[charging rate determined by form factor] is hard to do especially if the charger also does Lithium Ion.

Perhaps, but it is claimed to be done by Nitecore with it's universal charger SC4 (see "Intelligent Charging Mode").

And in the case of dedicated NiMH charger, like my own MW6178 Intercept, the charging rate is claimed to change based on form factor (via electrical properties). And, although I can't verify the charging rate, for about 10 years I've only had to insert a AA or AAA and let the charger go to work ... without having to press any buttons.

iamluck13

@iamluck13

I think the critical features are individual cell control, -dV/dt termination, and time termination as a backup (or for fast chargers, temperature termination).

I agree that those things are critical (but you might be suggesting that some of the other things I mention are not). On your prompting I will add "individual cell control". I don't like chargers that, for example, offer higher maximum charging rates in the outer cells only.

I'm not worried about a readout of voltage, although it can be nice to have.

Yes I'm inclined not to worry about voltage readout too much. Although as my knowledge expands I could see myself becoming more curious about it.

Regarding charge rate - rates above 0.5C are often recommended because the faster charger results in a more obvious -dV/dt signal. However, HKJ has tested even some like chargers like Panasonic BQ-CC17 as consistently properly terminating despite only charging at less than 0.2C

Yes that sort of thing is interesting. But generally HKJ seems to be testing with new cells. I wonder if the reliability for low charging rates remains for old cells. If a charger can prove they reliably terminate at rates < 0.5C then that may well count in favour of loosening my criteria. E.g. By allowing for a charger that uses at most 1000mA to charge the higher capacity Eneloop Pros (at about 2500mAh). Many chargers currently on the market appear to have a 1000mA maximum charging rate.

Slightly revised criteria

I revised the criteria slightly in virtue of the above discussion (and also due to other thoughts).

I now have 9 criteria instead of 7. I've added @iamluck13's "individual cell control" as "Per slot charging". I've added "No fatal flaw otherwise".

I've given a leading short name for the sake of referencing the criteria, which is followed by its definition. I've also ordered the criteria in rough order of importance (although getting that order right is not, in itself, important).

"-dV/dt termination with backups": Terminates by negative delta voltage (NDV or -dV/dt), with termination by temperature and timer, as backups.
"Zero charge post termination": On termination there is no charge.
"Visual termination alarm".
"Per slot display of: capacity, charging rate, and voltage": Per slot display of the basic battery values: present capacity in mAh or as a percentage of full; charging rate in A or mA; present voltage in volts.
"Per slot charging": The slots charge independently of what's happening with other slots. There's no requirement for pairing slots (e.g. The inner slots charge at a lower maximum rate than the outer slots).
"500 mA and 1500 mA charging rate": Configurable to charge to 500 mA and 1500 mA, for AAA and AA eneloops respectively.
"Configurable Form factor defaulting charging rate": The charge rate configuration needs to be done only once (if at all) and from then on the charging rate is determined by form factor (whether via physical dimensions or electrical properties).
"Audible termination alarm with optional off": An Audible termination alarm which can be toggled off through the settings. That is, so the audible alarm never triggers.
"No fatal flaw otherwise": Even if the above criteria are fulfilled there is no fatal flaw in the product pertaining to another issue (e.g. loud fan, bad companion applications) or manufacturer (e.g. bad customer support, the website makes your eyes bleed).

For the sake of reference I propose this criteria be known as the "Works Well Eneloop Charger Criteria". But perhaps there's a better name for it.

SkyRC MC3000

@fmc1. Thanks for mention of the SkyRC MC3000. Indeed I have been eyeing all three of the relevant SkyRC models: (Universal) MC3000, (NiMH/NiCd dedicated) NC2500, and (NiMH/NiCd dedicated) NC2600. They seem to come closest to fulfilling my criteria. I'll apply my (now 9) Works Well Eneloop Charger Criteria against the MC3000, to demonstrate what a review using my criteria might look like ...

Manufacturer Url: http://www.skyrc.com/Charger/MC3000_Charger
HKJ Review: http://lygte-info.dk/review/Review Charger SkyRC MC3000 UK.html
Battery Support: Universal

Works Well Eneloop Charger Criteria (Quotes from HJK's review unless otherwise stipulated) ...

Criteria	Result	Notes
-dV/dt terminations with backups	Pass	"A nice -dv/dt charging." ... "CAPACITY, CUT TIME and CUT TEMP are safety settings and can be used to terminate a charge on abnormal conditions." HKJ
Zero charge post termination	Pass	"TRICKLE C: Off, ..." HKJ
Visual termination alarm	?
Per slot display of: capacity, charging rate, and voltage:	?	Clarification needed. See below
Per slot charging	Pass	HKJ review shows "C.Current" configurable from "0.05A .. 3A". There's no indication the maximum 3A is not available to each slot (and variable for each slot). Manufactuer website shows " Charge current: Max. 3A (x4 slots)"
500 mA and 1500 mA charging rate	Pass
Configurable Form factor defaulting charging rate	Fail
Audible termination alarm with optional off	?	HJK Review shows a "Beep tone:" setting. Is this an audible alarm on termination?
No fatal flaw otherwise	Fail	The SkyRC apps get bad reviews: https://play.google.com/store/apps/developer?id=SkyRC%20Technology%20Co.%2CLtd.&hl=en

Works Well Eneloop Charger Criteria Results:

Passes: 4;
Fails: 2;
Unknown: 3;

Works Well Eneloop Charger Criteria Overall Result: fail.

Pros:

Exposes many configuration options via device, PC software, and Android App.
Dumps cycle data to csv file that you can manipulate in any program you like (if you don't like the PC native app).

Cons (to be determined): ....

the skyrc mc3000 hits 6.5 but not all 7

I (since revising my criteria) count it as 4 out of 9.

Correct me if I'm wrong but the SkyRC MC3000 appears to fail against:

"Configurable Form factor defaulting charging rate:" ground, as you mention (for which you are deducting half a point); and
"No fatal flaw otherwise" ... bad apps.

... and the following criteria are "unknown" by me (which you might be able to set straight) ...

Visual termination alarm.
Audible termination alarm with optional off.
Per slot display of: capacity, charging rate, and voltage ... a discussion below follows ...

On "Per slot display of: capacity, charging rate, and voltage" ...

HKJ mentions in their SkyRC MC3000 review

Generally the (advanced) user interface works fairly well, but I have one complain[sic]: ... I have just put 3 batteries in the charger and it shows this ...

... what will it do with the batteries? The second column shows some symbols, the arrow down is discharge and the * is break

in, but what chemistry, current (capacity for break_in) have I selected? I must either remember it, have a note besides the charger or use a few keypresses to check it.

So the lack of a display of the charging rate on the first screen might be a bit of a drawback. However, set against that is:

That charging current "C.Current" can be accessed a few screens deep.
There is a PC interface.
There is an Android interface.
What you've written could suggest that HKJ's con "I must either remember it ..." is not such a big deal. You create your program, memorize the meaning of your program, and switch to it. Is HKJ's concern that "I must ... remember it" overstated based on your having the model for some while?; and
Above all, from the promotional material it looks like we *can* display the charging rate (under the "Curr" column). See http://www.skyrc.com/image/catalog/product/charger/mc3000/8.jpg as found on http://www.skyrc.com/MC3000_Charger see "above a picture of Total Overview (TOV)". It looks like HKJ couldn't find the Total Overview screen or there's since been a firmware update. I mean can you confirm that I'm not confused here: Do I have it right that the "Curr" column displays the selected charge rate?

Edit 2017-10-22 01: SkyRC MC3000 Works Well Eneloop Charger Criteria, Text to Table format.

Edit 2017-10-22 02: Updated manufacturer link to SkyRC MC3000.

kreisl · Oct 21, 2017

I would buy the BT C3100 in your case.

Or the venerable Maha C9000.

They make things and usage easier.

( For specific questions\doubts re mc3k feel free to post\repost in HKJ's review thread

)
(( I am on vacation until the end of AO2018 ))

Written from my Xiaomi smartphone

a y tl;dr

fmc1 · Oct 21, 2017

Your unknowns should all be passes

Visual termination alarm.

There are three of them. The slot number button LED goes from solid red to solid green. The up arrow charge indicator reverses contrast from black over white to white on black. If you have the back light set to a time and not constant on or off the screen back light will come on.

Audible termination alarm with optional off.

With system beep set to on the charger will beep when a slot has finished charging. It will not beep if system beep is set to off.

Per slot display of: capacity, charging rate, and voltage ...

That's exactly what is displayed as long as a program is running. In the screen shot you show slots 1-3 are in the ready state, no programs are running.

As far a data explorer being a bad app, I simply disagree. Not only do I like it and find it useful, it's free.

Frank

John Bentley · Oct 24, 2017

SkyRC MC3000 Revisited

@fmc1 (Frank) On the SkyRC MC3000 thanks for the detail that changes the unknowns to passes.

On the apps getting bad reviews, I should have been clearer.

SkyRC MC3000 has three apps:

* An Android App: https://play.google.com/store/apps/details?id=com.Sky_mc3000
* An IOS App: https://itunes.apple.com/app/mc3000/id949072025?mt=8
* A PC App: As reviewed by HKJ at http://lygte-info.dk/review/Review Charger SkyRC MC3000 UK.html

The SkyRC MC3000 also has, as you'll know, an ability to dump charging data into a CSV file for consumption by any program that can take a CSV file (this is a great feature). HKJ also mentions this in their review.

As far as I can tell DataExplorer, http://www.nongnu.org/dataexplorer/, is a (free/libre) software that is not made by SkyRC. And I'm grateful for your informing me (us) that it is a good program.

My comment "The SkyRC apps get bad reviews" referenced all of SkyRC's Android Apps (including for other chargers made by SkyRC). The SkyRC MC3000 android app specifically, scores 2.5 ... quite the bad score, with reviews like

olly buxton. 2017-07-04. 1 star. Why has it taken so long to update this app and fix the save names come on this really effects the product experience pull your finger out devs......still no update 14/06/17

David W. 2 start. 2017-03-15. This new update broke the save programs section. Users can no longer create custom names for their charge/discharge profiles. The slot indicator does not report the correct slots in use. For example if you create a profile to use slot 1 and 4, the saved profile will report slot as 4, what about slot 1 shouldn't that be indicated as well. The battery resistance indicator is still not working properly. It is displaying "65535" which indicates a buffer overflow in the app.

From HKJ's review the PC app looks reasonably good. So that means configuration should be fairly easy (if one wants to avoid the UI on the device itself). And with a data dump available to Dataexplorer (or Excel) analysing data looks available to play with in an infinity of ways. So it seems one can work around the poor state of the Android Apps. I have no information on the quality of the IOS app.

Most chargers that I've so far looked at only have an on board UI. So that SkyRC provides a number of external UIs in addition could be argued as a bonus that shouldn't detract from scoring the charger, no matter how bad those external UIs are. However, that SkyRC seems to be systematically failing on the Android front leaves a bad taste.

So for the SkyRC MC3000 I'd revise the Works Well Eneloop Charger Criteria like this ...

Criteria	Result	Notes
-dV/dt terminations with backups	Pass	"A nice -dv/dt charging." ... "CAPACITY, CUT TIME and CUT TEMP are safety settings and can be used to terminate a charge on abnormal conditions." HKJ
Zero charge post termination	Pass	"TRICKLE C: Off, ..." HKJ
Visual termination alarm	Pass	"There are three of them. The slot number button LED goes from solid red to solid green. The up arrow charge indicator reverses contrast from black over white to white on black. If you have the back light set to a time and not constant on or off the screen back light will come on." (fmc1 above)
Per slot display of: capacity, charging rate, and voltage	Pass	"That's exactly what is displayed as long as a program is running. In the screen shot you show slots 1-3 are in the ready state, no programs are running." (fmc1 above)
Per slot charging	Pass	HKJ review shows "C.Current" configurable from "0.05A .. 3A". There's no indication the maximum 3A is not available to each slot (and variable for each slot). Manufacturer website shows "Charge current: Max. 3A (x4 slots)"
500 mA and 1500 mA charging rate	Pass
Configurable Form factor defaulting charging rate	Fail
Audible termination alarm with optional off	Pass	"With system beep set to on the charger will beep when a slot has finished charging. It will not beep if system beep is set to off." (fmc1 above)
No fatal flaw otherwise	Fail	The SkyRC Android apps get bad reviews: https://play.google.com/store/apps/developer?id=SkyRC Technology Co.,Ltd.&hl=en

Works Well Eneloop Charger Criteria Results:

Passes: 7;
Fails: 2;

Works Well Eneloop Charger Criteria Overall Result: fail (7 passes out of 9)

@Kreisl

For specific questions\doubts re mc3k feel free to post\repost in HKJ's review thread

As mentioned for current purposes I'm suggesting that specific chargers be looked at primarily to test my criteria, rather than the other way around. Of course, the motivating benefit is that applying my criteria to specific chargers (hopefully) sheds a new light on those chargers.

With that in mind let's have a look at applying the Works Well Eneloop Charger Criteria to the chargers you mention ...

Opus BT-C3100 V2.2

Manufacturer Url: None ?
Amazon: https://www.amazon.com/dp/B01852TBOU/?tag=cpf0b6-20 (4.4 stars on 133 reviews)
HKJ Review (for Opus BT-C3100 V2.1): http://lygte-info.dk/review/Review Charger Opus BT-C3100 V2.1 UK.html
Battery Support: Universal

Works Well Eneloop Charger Criteria:

Criteria	Result	Notes
-dV/dt terminations with backups	Fail	Uses CC/VV charging (HKJ Review). That might not be a bad thing ... this might challenge my criteria.
Zero charge post termination	Fail	"Note that the charger uses trickle charging when the main charge is finished, this is not really a good idea for LSD cells." (HKJ Review)
Visual termination alarm	Pass	Displays "Full" on the LCD. (HKJ review)
Per slot display of capacity, charging rate, and voltage	Pass	(But you have to press a button) "When charging or discharging it is possible to use the DISPLAY button to select between V, mA and mAh." (HKJ review)
Per slot charging	Fail	"Charge battery with 200 to 1000 (2000) mA. ... Using only slot #1 and/or #4, the maximum charge current is 2000mA. In all other cases the maximum charge current is 1000mA." (HKJ review) "The Charge rates for the Opus BT-C3100/BT-C3400 are 300mA, 500mA default, 700mA and 1000mA when you are charging 3 or 4 batteries. If slots 2 and 3 are empty, slots 1 and 4 can also be set to 1500mA or 2000mA in addition to the other four choices." fm1C below
500 mA and 1500 mA charging rate	Fail	"Charge battery with 200 to 1000 (2000) mA. ... Using only slot #1 and/or #4, the maximum charge current is 2000mA. In all other cases the maximum charge current is 1000mA." (HKJ review) "The Charge rates for the Opus BT-C3100/BT-C3400 are 300mA, 500mA default, 700mA and 1000mA when you are charging 3 or 4 batteries. If slots 2 and 3 are empty, slots 1 and 4 can also be set to 1500mA or 2000mA in addition to the other four choices." fm1C below
Configurable Form factor defaulting charging rate	Unknown
Audible termination alarm with optional off	Unknown
No fatal flaw otherwise	Pass

Works Well Eneloop Charger Criteria Results:

Passes: 3;
Fails: 4;
Unknown: 2

Works Well Eneloop Charger Criteria Overall Result: fail (3 passes out of 9)

Powerex (Formerly Maha) MH-C9000

Manufacturer Url: http://www.mahaenergy.com/mh-c9000/
HKJ review: http://lygte-info.dk/review/Review Charger Powerex MH-C9000 UK.html
Amazon: https://www.amazon.com/dp/B003DIGKOG/?tag=cpf0b6-20 (4.6 starts on 456 reviews)

Works Well Eneloop Charger Criteria:

Criteria	Result	Notes
-dV/dt terminations with backups	Fail	"The charger does not use -dv/dt termination, but constant voltage with a top off charge and has the temperature sensor as backup" (HKJ Review)
Zero charge post termination	Fail	"The charger uses about 2 hours to charge the battery, then it terminates on voltage and uses another two hours to top the battery, before it switches to a trickle charge. The charger will report done after the first two hours." (HKJ Review)
Visual termination alarm	Pass	"Done" on LCD screen (HKJ Review)
Per slot display of capacity, charging rate, and voltage	Fail	Displays only one slot at a time.
Per slot charging	Pass
500 mA and 1500 mA charging rate	Pass	"Normal charge of a battery, the current can be select from 0.2A to 2A in 0.1A steps." (HKJ Review)
Configurable Form factor defaulting charging rate	Unknown
Audible termination alarm with optional off	Fail	"There is no alarm indication when a cell terminates on high temperature. The C9000 simply terminates the charge and displays "Done" along with the charge time and mAh put into the cell" http://www.candlepowerforums.com/vb/showthread.php?154756-Maha-MH-C9000-Wizard-One-Charger
No fatal flaw otherwise	Fail	Ambiguous when full charge has been reached. See "Cons" below

Cons:

* "If you take your batteries out when the C9000 reports "done," they will not be fully charged. To get a full charge, you have to wait another couple of hours. Furthermore, the C9000 does not give a signal telling you when charging is actually finished. It is good to hear from you and MidnightDistortions that batteries will not be damaged if they are left charging too long, but it would be convenient to have a signal when they reach full charge. " <http://www.candlepowerforums.com/vb...r-do-I-need-(info-and-discussion-thead)/page3>
* "It is no surprise that some chargers uses a fan. This charger has no fan and do get rather warm when charging." http://lygte-info.dk/review/Review Charger Powerex MH-C9000 UK.html

Works Well Eneloop Charger Criteria Results:

Passes: 3;
Fails: 5;
Unknown: 1;

Works Well Eneloop Charger Criteria Overall Result: Fail (3 passes out of 9)

Charger Roundup conclusion

Given the current ranking against the Works Well Eneloop Charger Criteria ...

* SkyRC MC3000: fail (7 passes out of 9);
* Opus BT-C3100 V2.2: fail (3 passes out of 9);
* Powerex (Formerly Maha) MH-C9000: fail (3 passes out of 9);

... it seems misguided for you, @kreisl, to conclude "I would buy the BT C3100 in your case" and that the Powerex (Formerly Maha) MH-C9000 deserves veneration.

But thanks again for putting those chargers forward for scrutiny. I hope the Tennis was exciting.

Criteria conclusion

The criteria "-dV/dt terminations with backups" is subject to being overturned. That is, in principle a charger could use a charging method apart from -dV/dt so long as it reliably charged close to a battery's present capacity and didn't overcharge it.

However, as far as I can see -dV/dt is the best method for this. I rely on folks like HKJ:

[-dv/dt termination] is one of the best ways to termination a NiMH charge ....

That issue aside I'm not seeing any particular flaw in the Works Well Eneloop Charger Criteria.

Edit: 2017-10-26 15:28 Added comments by @fm1C on Opus BT-C3100 charging rate

iamlucky13 · Oct 24, 2017

You've been quite thorough about your research. If you need a new charger at the current time, it sounds like the SkyRC is your favored choice, so I don't see any real reason not to accept the drawbacks you have found and go with it.

With HKJ rating most of the chargers we've talked about as "good," and numerous happy users for each of them, I'm not really inclined to say any of them don't "work well," even if some of them do make design compromise that don't seem to make sense.

fmc1 · Oct 24, 2017

The Charge rates for the Opus BT-C3100/BT-C3400 are 200mA, 300mA, 500mA default, 700mA and 1000mA when you are charging 3 or 4 batteries. If slots 2 and 3 are empty, slots 1 and 4 can also be set to 1500mA or 2000mA in addition to the other four choices.

Kurt_Woloch · Oct 27, 2017

There's quite a bit of research going on in this thread, which I think is overdoing it. In fact, for now I've settled with a pretty primitive solution...

Until a few months ago, I had a Tronic charger which was € 8,99 and died after a few years, so I had to discard it. It worked for about 400 cycles on 2 cells, so that's about 800 cells charged. With a cost of € 8,99, that's 1.12 cents per cell charged.

The actual cells I'm charging are Eneloops, which cost me € 2,50 - € 3,12 (I bought two packs for different prices) per cell. If I (conservatively) count on each cell to survive about 500 cycles when charged in the Tronic (which had dv/dt termination), that's 0.5 to 0.6 cents per cycle on each cell. This is half the cost of the charger, so the charger cost twice as much as the batteries it charges.

Now I still have a working charger by Hama which I bought for € 2 at a thrift shop some years ago. This is a dumb charger which charges at a fixed 150-200 mA until you remove the cells, but it does the job for now. Even if that reduces the lifespan of the Eneloops to 300 cycles, it's still only 1 cent per charge per cell for the batteries. The only device where this really matters is probably my portable cassette player where the batteries get charged once a week, so the Eneloops would only last 6 instead of 10 years here. OK, this would increase their cost from € 0,94 to € 1,56 per year. On all other devices, the batteries only need to be charged at most 2-3 times a year if that, so the batteries in those will probably outlast me no matter if they last for 300 or 500 cycles (if they don't die by old age before that anyway).

If I'd get a new charger now, its only purpose would be to prolong the lifespan of the batteries, which doesn't make much sense given the circumstances above. Still, if or when I'll eventually need new AA rechargeables or the Hama charger breaks as well, I'll probably buy one of the bundles Panasonic offers including batteries and a (fairly) smart charger. There's still the question if it's gonna pay off because you don't know how long it will be until the charger breaks again, so on correct calculation you might find it has eaten up the savings from the batteries again.

It does make sense to use rechargeables instead of Alkalines, but unless you use and recharge them very often, in my opinion it's not worth it to invest in a really good (and expensive) charger. At least for me it isn't.

John Bentley · Oct 28, 2017

@ Kurt_Woloch

There's quite a bit of research going on in this thread, which I think is overdoing it.

I don't think you mean what you've written. This is, like any tech form, a forum chiefly for the provision of research. Moreover, you've (with thanks) provided "quite a bit of research" of your own. So unless you think you've written as you shouldn't: I think you mean something else. That is, I think you mean that (in the light of your whole post), in the circumstances that apply to folks like you (not charging very often), the overriding criteria should be cost.

I don't agree but I don't think it important to settle that disagreement. I think the value of your post is in the implicit suggestion that the cost of the charger might be an important criteria to throw into a standard review.

@fm1C (Frank) thanks for the info on Opus charging rates. I've added that to the table above for the Opus BT-C3100.

@Iamlucky13

If you need a new charger at the current time, it sounds like the SkyRC is your favored choice, so I don't see any real reason not to accept the drawbacks you have found and go with it.

One reason would be the existence of another charger that matches or beats the SkyRC MC3000 score.

The candidates that come to mind are SkyRC's own NiMH/NiCD chargers, the NC2500 and the NC2600. So let's see how they fair against the Works Well Eneloop Charger Criteria:

SkyRC NC2600

Manufacturer Url: http://www.skyrc.com/Charger/NC2600_Charger
Amazon: None with review
HKJ Review: http://lygte-info.dk/review/Review Charger SkyRC NC2600 UK.html. ( 1.5 stars from http://lygte-info.dk/info/roundCellChargerIndex UK.html)
Battery Support: NiMH/NiCD
Image: http://www.skyrc.com/image/data/980px_en/NC2600/1.jpg

Works Well Eneloop Charger Criteria

Criteria	Result	Notes
-dV/dt terminations with backups	Fail	Unreliable charging "Slot #2 and #3 looks the same [terminating with -dV/dt], but #4 looks like the charger terminated due to [threshold] voltage" (HKJ Review).
Zero charge post termination	Fail	"This curve looks like the charger uses -dv/dt to terminate, then a top-off charge and finally a trickle charge." (HKJ Review). Purports to turn off trickle charge (but not top off charge?) via Android App http://www.skyrc.com/Charger/NC2600_Charger, but Android App is buggy (https://play.google.com/store/apps/details?id=com.skyrc.nc2600&hl=en).
Visual termination alarm	Pass	"Done" on LCD. http://www.skyrc.com/Charger/NC2600_Charger
Per slot display of capacity, charging rate, and voltage	Pass	"Large LCD display with backlight for easy reading. It digitally displays the various operation modes,also the charging current (in mA),charged capacity (in mAh),voltage (in Volt) and elapsed time (in hh:mm)." http://www.skyrc.com/Charger/NC2600_Charger
Per slot charging	Pass	"Four Independent Slots" http://www.skyrc.com/Charger/NC2600_Charger
500 mA and 1500 mA charging rate	Pass	"Normal charge with selected current (200-2600mA)" (HKJ Review).
Configurable Form factor defaulting charging rate	Unknown
Audible termination alarm with optional off	Unknown
No fatal flaw otherwise	Fail	+ Buggy app: https://play.google.com/store/apps/details?id=com.skyrc.nc2600&hl=en "The charger is fairly good without the application, but if the application had worked it would have been better." (HKJ Review)

Other Comment:

Loud fan: "The fan starts when required and can be heard for some distance (Couple of meters)" (HKJ Review). It's not clear whether the fan is silent during regular charging or starts up (and is loud) during exceptionally high charging rates.

At the time of HJK's test, reliable termination with -dV/dt didn't occur. That alone would rule it out.

Works Well Eneloop Charger Criteria Results:

Passes: 4;
Fails: 3;
Unknown: 2;

Works Well Eneloop Charger Criteria Overall Result: Fail (4 passes out of 9)

SkyRC NC2500

Manufacturer Url: None.
Amazon: None with review
HKJ Review: http://lygte-info.dk/review/Review Charger SkyRC NC2500 UK.html (2 stars from http://lygte-info.dk/info/roundCellChargerIndex UK.html)
Battery Support: NiMH/NiCD
Image: http://lygte-info.dk/pic/SkyRC/NC2500 charger/DSC_4179.jpg

Works Well Eneloop Charger Criteria

Criteria	Result	Notes
-dV/dt terminations with backups	Unknown	Probably passes but unclear if back up termination available. "With NiMH batteries I will either use -dv/dt termination and no trickle charge or"(HKJ Review) "The metal at the side is probably the temperature sensor." (HKJ Review)
Zero charge post termination	Pass	You can turn the trickle charge off through the Android APP, if you can get the app to work (See HKJ Review).
Visual termination alarm	Pass	"The full display with everything on, notice the DONE indicator" (HKJ Review)
Per slot display of capacity, charging rate, and voltage	Pass	See LCD images in HKJ Review.
Per slot charging	Unknown	HKJ has a curve charging at 2500mA. But it is unclear if this is there is a limit on the charging rate if all four slots are used. Otherwise the slots appear to be Independent: "When a battery is put into a slot, the function must be selected for that slot. This must be done for each slot when filling them. If nothing is done the charger will start charging with the last selected current after some seconds." (HKJ Review)
500 mA and 1500 mA charging rate	Pass	"Normal charge with selected current (200-2500mA)" (HKJ Review)
Configurable Form factor defaulting charging rate	Pass	Apparently it passes: "When a battery is put into a slot, the function must be selected for that slot. This must be done for each slot when filling them. If nothing is done the charger will start charging with the last selected current after some seconds." ... "The battery minus connections is in two steps, one for AA and one for AAA, the charger knows what size battery is in it" (HKJ Review)
Audible termination alarm with optional off	Unknown
No fatal flaw otherwise	Fail	+ Poor Android App "The app has some good possibilities, but it can be a problem getting it working." (HKJ Review) "The charger itself seems to work as it should, but the Bluetooth hardware, or the app, is rarely working, and refuses to connect. " (https://play.google.com/store/apps/...WWQ5UUk0bG1jN0VKZUFheFJGUmcwREtSOGFLb1E&hl=en). Android App Google Play Page: https://play.google.com/store/apps/details?id=com.revogi.smartcharge&hl=en

Other Comment:

"The fan starts when required and can be heard for some distance (Couple of meters)." (HKJ Review). It's not clear whether the fan is silent during regular charging or starts up (and is loud) during exceptionally high charging rates.

Works Well Eneloop Charger Criteria Results

asses: 5;

Fails: 1;
Unknown: 3;

Works Well Eneloop Charger Criteria Overall Result: (5 passes out of 9)

Conclusion

Of the chargers so far examined ...

SkyRC MC3000
Opus BT-C3100 V2.2
Powerex (Formerly Maha) MH-C9000
SkyRC NC2600
SkyRC NC2500

... none pass.

However, the SkyRC NC3000, a universal charger, appears to be the least bad.

Among the NiMH/NiCD dedicated chargers, the SkyRC NC2500 seems to beat the SkyRC NC2600, even though the NC2600 is meant to be an update to the NC2500.

Moreover, from a (somewhat casual) survey from among all on HKJ's review summary page (http://lygte-info.dk/info/roundCellChargerIndex UK.html) there doesn't appear to be another contender.

So, from among the failed chargers, the two best options seem to be:

SkyRC NC3000, a universal charger: (7 passes out of 9); or
SkyRC NC2500, a NiMH/NiCD charger: (5 passes out of 9).

SilverFox · Oct 29, 2017

Hello John,

Welcome to CPF.

In any discussion of chargers you need to also pay attention to your intended usage. In charging everything is a compromise and you have to choose the best fit for your application.

I have been extremely pleased with 3 chargers that I have used with my Eneloop cells.

The Duracell 15 minute charger along with the Enegerizer 15 minute charger were excellent. They never missed a termination and rapidly provided me with cells ready to use at a moments notice. In emergency or some industrial applications were speed is important, this is the direction to go. The trade off is reduced cycle life.

The ultimate charger in my perspective is the Schulze line of hobby chargers. They are designed for battery packs but I have used mine with individual cells. The Auto mode takes a little more time and seems to base termination on internal resistance or the slope of the cells voltage curve. It pauses and measures several times during the charging process. The advantage is that the cell doesn't heat up and you end up with maximum capacity from the cell along with maximum cycle life. With the move in the hobby RC industry to Li-Ion chemistry, Schulze went out of business. The cost for advanced NiMh algorithms was no longer an advantage and their chargers ended up being too expensive for the general market.

My current favorite is the MAHA C9000. You have some limited information in its termination methods. From the MAHA FAQ page I find...

"How does the MH-C9000 detect end-of-charge signals from the batteries?

The MH-C9000 uses a combination of Negative Delta V, Zero Delta V, Peak Voltage, time and temperature to determine the end-of-charge. In addition, proprietary algorithms are used."

Most of the time at lower charge rates you will hit the peak voltage and terminate on that as HKJ observed in his testing. However if you step the current up to 2000 mA you will more frequently see a -DV or 0 DV termination. Charge some older cells with higher IR and you see temperature termination.

Keep in mind that charging NiMh cells involves higher voltages. It is not uncommon to see a cell voltage in the 1.52 - 1.56 voltage range at termination. MAHA chose to terminate the charge at 1.47 volts and then follow it with a 100 mA top off charge for 2 hours. During that 2 hours the cells voltage does increase to around 1.54 volts indicating a full charge. Pulling the cell at DONE gives you about 90% of maximum capacity. Once again there is a trade off. Treat the cells gently during charging gives you more cycles from the cell, but if you need them quickly you end up with slightly reduced capacity.

The SkyRC MC3000 brings programming features to charging. I can program it to something similar to the MAHA C9000 and tweak the settings to my preferences. I like this and if it holds up I anticipate it replacing my MAHA chargers.

Bells and whistles aside, a charger should be viewed by how it treats the cells it is charging. If you are pushing the limits you want to make sure that there are no missed terminations. If you have more time to charge you can look for optimum cycle life. Cost factors and marketing can add other useful features but the primary concern is the charge.

Tom

Kurt_Woloch · Nov 4, 2017

John Bentley said:
@ Kurt_Woloch

I don't think you mean what you've written. This is, like any tech form, a forum chiefly for the provision of research. Moreover, you've (with thanks) provided "quite a bit of research" of your own. So unless you think you've written as you shouldn't: I think you mean something else. That is, I think you mean that (in the light of your whole post), in the circumstances that apply to folks like you (not charging very often), the overriding criteria should be cost.

I don't agree but I don't think it important to settle that disagreement. I think the value of your post is in the implicit suggestion that the cost of the charger might be an important criteria to throw into a standard review.

Yes, I agree that it seems pretty ironic that I write so much while at the same time stating that it's overdoing it. This is probably an expression of an inner conflict of mine. The problem is that my parents grew up during World War II when here in Austria, there was extreme scarcity in everything (as they told me). Thus there's a deep feeling in them that you should, if ever possible, avoid having to buy anything... and batteries, back then, were very expensive, relative to the money my parents had, and you shouldn't waste those batteries. Back then there were only zinc-carbon batteries, no alkalines and no small rechargeables. So think of a situation where you have don't have access to rechargeables, but have to buy zinc-carbon batteries for about $10-20 for a 4-pack of AA's, and a 4-pack of rechargeables would probably be $200 or more. If batteries are that expensive, you will take care not to waste them. My parents also taught me that you should carefully examine every purchase and that if things break, something severe went wrong, and you should try to find out what the mistake was and not make it again.

Now I know that batteries aren't that expensive anymore, but from that comes my tendency of analyzing everything in great length even if it's probably not worth it.

Yes, I agree that the price of the charger is an important point in a review, but so would be its longevity. Trouble is, you can't easily tell how long a charger will last. The Tronic charger I mentioned seemed to be built rather solidly until it broke. And there are repeatedly reports of the Maha C-9000 breaking in some way (one slot after another) making me wonder if this charger is really worth it.

Unfortunately, it seems to me that electronics become more fragile these days and break without any apparent reason, the real reason being electrolyte capacitors failing or something like that. Seems to me like modern switching power supplies, as cheap and efficient as they are, are more prone to such failures than old heavy transformers, and if they break, they often render a whole device bricked.

Anyway, as for chargers, there are more criteria which would actually be important:
1. The ease of the charging procedure... this is important because you have to go through it every time you're charging the batteries. The easiest one would be just dropping in the batteries and having them charged.
2. The standby power consumption... because a low standby power consumption allows you to keep the charger plugged in at all times without incurring huge additional power costs, thus shortening the charging procedure.

joelbnyc · Nov 10, 2017

OP says there is no hard evidence for charging at the lower or upper end of the 0.5C to 1C spec, but I thought there was plenty of evidence that fast charging reduced lifecycle.

Battery specs involving use don't necessarily state what is optimal, right, moreso what the manufacturer thinks is acceptable for consumer behavior.

John Bentley · Dec 9, 2017

@Kurt,
------

Thanks for your further thoughts.

> Yes, I agree that the price of the charger is an important point in a review, but so would be its longevity.

We'll I was suggesting that you seemed to be advocating strongly for the price of the charger as important. I thought (and think) other criteria more important ... indeed in part because a cheap charger that breaks early might, in the long run, end up costing you more.

So I think the longevity of a charger, that the electronic unit is well built, and the manufacturer has good quality control, more important. In this way I'd share the values you've lately promoted ...

> so would be its longevity .... [out of order] My parents also taught me that you should carefully examine every purchase and that if things break, something severe went wrong, and you should try to find out what the mistake was and not make it again.

You also wrote:
> Thus there's a deep feeling in them [Kurt's parents] that you should, if ever possible, avoid having to buy anything.

I'd agree with this (fortunately without having to go through the deprivations of WWII). It is better to make your life simpler by not buying something you don't need. For every object you purchase brings with it a set of time consuming tasks. The corollary is: if you do buy something you ought buy something fit for purpose and well made ... to minimize the time spent managing the new object.

And so I'd entirely agree that "The ease of the charging procedure" is a significant criteria. But I think that criteria has been implicit across all of the 9 criteria I've tabled. If a charger passed all that criteria we should expect, once configured, to be able to drop in cells, have them charge until an alarm goes off, at which point you remove your cells. This is how my present MW6178 Intercept charger behaves (however I no longer have confidence it will handle my newly purchased Eneloop pros).

It is also good of you to put on the table the criteria standby power consumption. Perhaps like many I tend to leave various appliances plugged in and turned on. And, like many, I ought be thinking in greater detail about the total vampire energy that wastes.

@ joelbnyc
----------
> OP says there is no hard evidence for charging at the lower or upper end of the 0.5C to 1C spec, but I thought there was plenty of evidence that fast charging reduced lifecycle.

Battery specs involving use don't necessarily state what is optimal, right, moreso what the manufacturer thinks is acceptable for consumer behavior.

My guess matches with yours, that the manufacturers aren't necessarily revealing what is optimal when they stipulate a 0.5 to 1C range, just what is acceptable. And we freaks would like to know what's optimal.

As I originally mentioned panasonic (and folks like Silverfox) have expressed a preference for the 1C end. But that's just to ensure a good termination. The issue is: if a charger is sure to terminate properly at either end, which is optimal? If you can link to any evidence that claims (at least) and proves (ideally) that one end of the range is optimal, that would be informative.

In the meanwhile I think we need to be careful about the ambiguity of the term "fast charging" as in "but I thought there was plenty of evidence that fast charging reduced lifecycle". In a mobile phone context, with Lithium Ion batteries, I've measured a "fast charger" at 6 times faster than when using wireless charging. Here, when discussing either 0.5 to 1C in a NiMh context, either seems to be referenced as a "Rapid charge current" (e.g. as in https://na.industrial.panasonic.com/...iles/panasonic_nimh_chargemethods.pdf, p12).

The evidence you have in mind might apply to the mobile context, with respect to Lithium Ion batteries. However, I'm unclear myself on this issue. Intuitively a faster charge is going to be less optimal. But that might be negligible between 0.5 and 1C in a NiMh context. Again, the way to settle this is with hard data.

@SilverFox
----------

Many thanks for your welcome. I've been fleetingly lurking at CPF for a few years and found your posts to be very informative, as your post above is. Naturally I have some follow up questions and points.

Firstly, in your experiment from a while back, which I earlier quoted (from [Eneloop Charging Rate, post 37](http://www.candlepowerforums.com/vb...harging-Rate&p=2376831&viewfull=1#post2376831)) ...

>... I set out to see if I could get 500 cycles from a set of batteries. I took 9 cells in a battery holder and ran a test. The cells were 2400 mAh capacity. I charged them at 2.5 amps and discharged them at 1.0 amps down to 1.0 volts per cell. Every 50 cycles, I ran a 16 hour balancing charge. The cells barely warmed up during charging. The charger never missed a termination because I had the charge quantity set to 2650 and the charger never terminated on quantity. At 653 cycles I terminated the test. The capacity had dropped below 80% of its initial capacity, and that is my criteria for termination.

> I followed the manufacturers recommendation and charged at 1C. I got more than the advertised 500 cycles from my set of 9 cells. I think charging at 1C works well, and I highly recommend it.

... what was the chemistry? NiCd?

You mention choice with respect to "the best fit for your application". I agree the context of the intended application will change the criteria.

I think I have in mind with my 9 criteria a context of charging batteries so as to optimize their life (without necessarily having to be too exacting about this all the time) and either:
* Features to satisfy someone who is starting to care about battery cycle optimisation to the extent where they are starting to have to, and want to, learn about arcane knowledge about batteries; or
* Someone who wants to easily use a charger without too much thought at all.

That is, I'm not, for example, looking for a charger that (only or by default) charges at maximum speed.

Thanks for mention of the Schulze line, now unavailable.

Thanks for going over the MH-C9000.

Having a closer look at their website I discover a few things.

Firstly, and incidentally, they don't appear to be "formerly maha", as I previously alleged. Rather they just seem to have schizophrenic branding "Founded in 1993, Maha Energy Corporation is a global leader ... In addition to PowerEx brand products, a significant percentage of Maha Energy's revenue is generated from OEM & custom manufacturing businesses".

Secondly their Faq, which you reference, contains a few interesting things ...
> The recommended charging current is 0.5C, or 0.5 times the battery capacity

Clearly they favour the lower end of the 0.5 to 1C spectrum.

It is very good of you to focus my (and our) attention on the MH-C9000's termination methods. The termination profile mentioned in the FAQ, your (very helpful) description of the termination, and [HKJ's test](http://lygte-info.dk/review/Review Charger Powerex MH-C9000 UK.html) seem consistent with each other. (Excepting HKJ's 2000 mA test "looks like the termination is still done on [threshold] voltage", where you tell me " if you step the current up to 2000 mA you will more frequently see a -DV or 0 DV termination" ... I'm glad for your providing in more information here).

I certainly don't have enough knowledge to about termination methods in general to be confidently dismissive of some proprietary approach. So that, looking at HKJ's tests, the MH-C9000 tends to use threshold voltage ('peak voltage' I assume is what they call it) with a top off charge, rather than negative delta voltage ... I'd be willing to be persuaded this is not a bad thing. (I note they claim to use "a combination of Negative Delta V, Zero Delta V,Peak Voltage, time and temperature to determine the end-of-charge" ... and you've verified that they sometimes use some of the methods from that list).

And so, do I read you right, that you are attempting to persuade by pointing to a charge to 90% capacity as being a good thing if you want to optimize the batteries life?

For Li-Ions there seems to be advice from some authorities that, for a long life, you would aim to charge between 30% and 80% of charge (against new max); and aim for 70% max if you want to optimize to the extreme. E.g. ...

> What would be best for the battery long term.. 90%->40% charge daily, or 80%->30% ? https://twitter.com/cairnz/status/448403837242851328 ...

> 80% to 30% (Elon Musk) https://twitter.com/elonmusk/status/448466037441179649

.
> Tesla recommends to only daily charge to 90% capacity and to charge to 100% only when needed for long trips. … [but] Jeff Dahn, a renowned battery researcher and the leader of Tesla's research partnership through his battery-research group at Dalhousie University, … suggests going even lower … if someone wants to really push the optimisation to its limit, … ""I would recommend charging to 70% normally. When you need a long trip, charge to 100%."" https://electrek.co/2017/09/01/tesla-battery-expert-recommends-daily-battery-pack-charging/

... But I can't find anything for NiMh with an assertion that charging below max is good for long term capacity. Do you have a source?

AA Cycler · Dec 9, 2017

John Bentley said:
Intuitively a faster charge is going to be less optimal. But that might be negligible between 0.5 and 1C in a NiMh context. Again, the way to settle this is with hard data.

I tested how low (0.5A) and high (1.5A) charge/discharge currents affect the life cycle of NiMH batteries (Varta 2100). No scientific data, just a test of a curious person.

You can think of it as a 0.25C vs 0.75C comparison. The results confirm your thoughts - only negligible difference between 0.25C and 0.75C. I have not tested 1C or above, so I cannot tell...

John Bentley said:
... And so, do I read you right, that you are attempting to persuade by pointing to a charge to 90% capacity as being a good thing if you want to optimize the batteries life? ...

... But I can't find anything for NiMh with an assertion that charging below max is good for long term capacity. Do you have a source? ...

In my Charge and Energy Efficiency test I show that NiMH batteries have 100% coulombic-efficiency up to 90% state of charge. I believe that above 90% SoC other irreversible chemical reactions start happening that harm the battery and shorten their lifespan. I believe that one must stay withing the 100% charge efficiency region (0%-90% SoC) to optimize for battery life. Thought I don't have evidence to prove that...

Cheers,
AA Cycler

AA Cycler · Dec 9, 2017

John Bentley said:
Summary

I offer that an Eneloop (low self-discharge Nickel Metal Hydride (NiMH)) charger must have the following features in order to be regarded as "working well" and not "flawed":

Configurable to charge to 500 mA and 1500 mA, for AAA and AA eneloops respectively.

The charge rate configuration needs to be done only once (if at all) and from then on the charging rate is determined by form factor (whether via physical dimensions or electrical properties).

Terminates by negative delta voltage (NDV or -dV/dt), with termination by temperature, then timer, as backups.

Per slot display of the basic battery values: present capacity in mAh or as a percentage of full; charging rate in A or mA; present voltage in volts.

Visual termination alarm.

Audible termination alarm which can be toggled off through the settings.

What do you reckon?

It's funny that I ended up with very similar criteria for may "dream analyzing charger" as you did for your Eneloop charger. These are the things we share in common:

* form factor based fixed charge rates
* favoring simplicity and reliability: no moving parts, no high currents, simple electronics, robust build
* 0dV termination (which is basically just a special case of -dV/dt termination) with temperature and timer backup
* per slot display
* visual termination alarm

In my search for perfect analyzing NiMH charger I ended up using OPUS BT-C700 and will use it until I find something that is closer to my ideal... But I shut up now, I don't want to hijack this thread of yours...

Cheers,
AA Cycler

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