Want to ask a question to an official ENELOOP technician? Please post them

[ChibiM]

Round 2:
The interview questions and answers for the Eneloop technicians are on the website. Until I have more time to put them 1 by 1 in the correct section on the website they can be found here: https://eneloop101.com/interview-with-eneloop-technicians/

 

[NiMHi]

Interesting. Thank you.

I made a summary (about the stuff I find interesting):

Difference between old and new generation Eneloop is that the process of manufacturing and raw materials improved.
Difference between Eneloop and Eneloop Pro is a thinner canister for Pro and a different ratio negative and positive electrode material.
More negative than positive material gives higher capacity but also more stress which causes faster higher internal resistance and lower cycle life.
Difference in Eneloop from China and Japan is that in Japan the machines were a very high investment to get the best possible machines.
Only one NiMH factory in Japan.
Lifetime of 10-15 years wouldn't be a problem.
For charging the maximum voltage isn't too important (<1.6V). Preferred charge rate is 0.5C.
Overdischarge is worse than overcharging which isn't as bad.
Temperature is best to keep low (30C sweet spot). 40-50 degrees Celsius is no problem. >60 degrees Celsius will give noticeable reduction in cycle life.
Deep discharging (< 0.8 or 0.9V) causes faster higher internal resistance.
Break-in charges and refresh charges are not recommended. Some people would gain a few % of capacity.
State of charge (SOC) of new Eneloops is 100% in Japan, 70-75% worldwide. Batteries are first charged and then discharged to 70% for extra long shelf life.
Dumb and cheap chargers still exist so people can move from alakaline to rechargeable for low cost.
There is no way to recover from (extremely) high internal resistance.
Best way to store Eneloop for a long time is in a cool environment (around fridge temperature) with a 20-30% state of charge.
Best way to achieve the 20-30% is by first charging to 50% and then discharging.
Not much new research on the horizon. Current research focus is on minimizing the large drop (voltage?) from 100 to 90% and improve LSD capabilities.

 

[KITROBASKIN]

The summary is appreciated. Anyone else care to bring up other information they find interesting?

 

[archimedes]

The information about eneloop vs eneloop Pro is especially appreciated, thanks for summarizing above.

 

[WalkIntoTheLight]

Things I found surprising:

1. Over-discharging is way worse than over-charging. And, over-charging isn't really that bad. The common wisdom around here seemed to be that over-charging was really bad for Eneloops, but it seems like that might be wrong.

2. Best storage is at only 20%-30% of charge, and in the refrigerator. I'm surprised it's so low, and I have always stored at 100% charge at room temperature, without much degradation it appears. Of course, the techs didn't say how much better a low charge and low temperature is.

3. When storing, first charge them up, then discharge down to 20%. Well, that's just weird.


I think I'll still keep them 100% charged when in storage. It doesn't seem to hurt them much, and it's way more convenient. I already have to baby lithium-ion batteries in storage, I don't want to have to do it for NiMH.

 

[ChibiM]

Thanks NiMHi for putting that all in a summary, with normal readable English

Just keep doing what you are doing Walkintothelight. These are just best practices. He would recommend charging to 50% and then discharging to lets say 40% instead of charging to 40% and then stop and store them. No need to go to 100% and then discharge to 30%.

You are correct, because its best practice, they didnt tell the % of difference there would be. It was more of long-term storage. You don't need to baby them, I think eneloops are probably the most 'mature' batteries out there

 

[MidnightDistortions]

I'm a little late to the party but some interesting answers here. I could understand overdischarging would be worse than overcharging but i have only gotten an Eneloop to 0.4 volts. I've done some NiMh cells into the negatives before and the cells were noticeably worse afterwards.

I could see storing Eneloops at 100% wouldn't be entirely safe as regular NiMhs would degrade at that point. Most of my LSD cells are stored at 70% or so. I wonder if the method the technician suggests is for long term storage, like you don't plan on using for 10 years or so.. if you're going to use them within a few years storing them at 70 or 80% would be fine as you'll probably need to use them right away in a pinch.

 

[marcosg]

Hello,
Is there a way to translate the storage percentage to Volts?
Lets say 50% = 1.5V? Considering they are fairly new Eneloops.
Also, would the recommended storage voltage or percentage would be the same for the AAA's and the Eneloop Pros?
I'll be using the C9000 along with a multimeter to prepare them for a long term storage.
I could also open a new package and see their voltage and match the opened ones to that, right?



Thanks


Just found this info.
https://main.panasonic-eneloop.eu/en/news/storing-batteries
[h=2]Charge levels[/h]Always check the charging level before the battery storage. Use separate containers to keep new and used batteries apart. The Nickel-based batteries (like the eneloop batteries) can be stored at any state of charge. The Lithium Ion ones must be stored at 30-50% maximum charge for the best results. But it's better to store when they are fully charged when you're not going to recharge in a few months.

 

[NiMHi]

Hello,
Is there a way to translate the storage percentage to Volts?
Lets say 50% = 1.5V? Considering they are fairly new Eneloops.
Also, would the recommended storage voltage or percentage would be the same for the AAA's and the Eneloop Pros?
I'll be using the C9000 along with a multimeter to prepare them for a long term storage.
I could also open a new package and see their voltage and match the opened ones to that, right?



Thanks

The voltage curve of NiMH (LSD) is rather flat and so it is difficult to estimate the capacity based on voltage alone. Here you can see the voltage curves: https://lygte-info.dk/review/batteries2012/Eneloop AA BK-3MCCE 1900mAh (White) UK.html

My guess, no guarantee, is that when the voltage really starts to go below the flat voltage level (which depends on the load) you get into the 20-30% charge state. So just below the 1.20-1.25 Volts.
However, if the battery has time to recover the voltage might be different than under load.

Another way is to look at the voltage during charging from flat. See the last graph on the page I linked above. With a 1 Amp charge current stop around 30 min charging for 20-30 state of charge.

Edit: I just now read your edit. Okay... that is a different option.... just charge full for storage. Not sure if that storage is the same as long storage.

 

[marcosg]

Thanks NiMHi,
I'm bad with math, but I did a test to get to a closer number.
Did I test last night with an old package (+- 4 years old).
Out of the package they were about 1.3 Volts, then I did a discharge = 1200mAh
So, for storage purpose, 1.3 Volts to 1.35 Volts ball park would be ok I guess if is my math is right.
That's about 60% of it's capacity.
However, I would still love to hear from the folks here with far more experience than mine.
I have about 85 AA's and 50 AAA's to store.

 

[Gauss163]

The voltage curve of NiMH (LSD) is rather flat and so it is difficult to estimate the capacity based on voltage alone. Here you can see the voltage curves: https://lygte-info.dk/review/batteries2012/Eneloop AA BK-3MCCE 1900mAh (White) UK.html [..].

That's not really the culprit since that could be solved with more accurate measurements. Rather, the main culprit is that NiMH has extremely high voltage hysteresis, so SOC depends not only on resting voltage but also on the recent history of (dis)charges - i.e. the path taken to reach the voltage, e.g. see the graphs here. That's why fuel gauges like the ZTS tester can only give very crude estimates - often off by 50% or more. Otoh, Li-ion has much lower hysteresis so one can get very good SOC estimates from resting voltage.

 

[SilverFox]

Hello Gauss163,

Are you aware that the ZTS uses voltage under a specific load? This still results in some error because there are using a look up chart for the most popular NiMh cells and not specifically low self discharge cells. The low self discharge cells seem to hold higher voltage under load that that throws the ZTS readings off. Also, if your use involves loads different from what the ZTS uses there will be some error.

Tom

 

[Gauss163]

Are you aware that the ZTS uses voltage under a specific load?

Of course, but that doesn't solve the problem. It's still extremely inaccurate as will be any generic NiMh capacity tester - see earlier discussion here. There are ways to improve accuracy of NiMh fuel gauges dedicated to a single pack (so it can be tuned to the specific chemistry and can track various parameters)., but this is not possible in a general purpose capacity tester used on many different cells. There is no hope of attaining good accuracy in that case. It is simply not theoretically possible.