# Please share your experiences with rechargeable 9v batteries.



## UserName (Dec 31, 2014)

I've been using eneloops in everything I can get them to fit, including adapters to fit c and d type devices, for several years now. I've been charging them with C9000, and I think I've had outstanding results from them. A few AAA's are showing reduced capacity, but I haven't had a single cell out of probably a total of 100 that needed to be scrapped, in many years now. 

However, I'm still buying alkaline 9v batteries. I get the big duracell packs at costco to economize, but I still don't care for the recurring expense. I'm also down to my last two, so if I'm going to investigate other alternatives, the time to do it is now. 

Recommendations? 

I'm open to any chemistry, but I do not want 7.2 V cells like the old NiCd ones used to be. 8.4v I could maybe settle for, 9.6V sounds better.

Low self discharge will probably be top priority, followed closely by cycle life/reliability.

I did some searching to see if there was such a thing as a maha c9000 style of charger/analyzer for 9v batteries, and have come to the realization that because it is an actual *battery* (series of cells), such a charger which works on the individual cell basis is not a possibility. Still, I'd be interested in knowing which chargers are the most beneficial toward the long term cycle life of the batteries.

Intended usages will be mostly smoke detectors, and test meters (DMM, digital amp clamp, etc.) Common alkalines in this usage typically give a service life in excess of a year, and for serious consideration, I need rechargeables that will last at least that long, meaning LSD, and capacity comparable to or better than an alkaline.


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## AB8XL (Dec 31, 2014)

Between work and home I have 26 of the 9.6v Powerex Imedion LSD batteries along with their chargers MH-C1090F and MH-C490F. I find that they perform well using them in DMM's, Infrared Thermometers, LCR Meters, Current Probes, Fiber Optic Transceivers, old transistor radios and dog collars. 

I haven't used them in smoke detectors yet, I don't have that level of confidence in them since I haven't done any long term testing with them.


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## WalkIntoTheLight (Dec 31, 2014)

I have been using rechargeable 9 volt NiMH batteries for about 12 years. My original bunch were Powerex 200 mAh batteries, 8.4v nominal (composed of 7 AAAA cells), obviously not low-self-discharge. Out of 8 batteries, 3 are still working. When one dies, it is because 1 of the AAAA cells has died, which results in lower voltage for the battery, and high resistance. I scrap the battery at that point. I was never too careful with how I treated these batteries, because I don't have a smart charger for them. I have a timed charger that charges at 30mA. I'm sure I overcharged them every time.

Recently, I've purchased some Tenergy Centura 200mAh low-self-discharge 9 volt NiMH batteries, again with 8.4v nominal. After charging, they settle down to about 9.2v after a few weeks of resting. I expect like most NiMH cells, they'll have a gradual voltage slide down to about 8.4v when they're empty. This appears to be plenty of voltage for everything I've used them for: smoke detectors, multimeter, motion detectors, door opener, etc.

Tenergy does sell an inexpensive charger they claim is "smart". I'm sure it doesn't charge the individual cells in the battery, but it likely limits overcharging.

I have also bought a couple of Energizer Recharge 9v batteries, 175mAh. These aren't LSD, but appear to last a few months between charges.

9 volt rechargeables are about 4x the price as quality alkalines. I except them to last about 8-10 years, so to make it economical you should probably use them in devices that require new batteries at least every 2 years. Perhaps not worthwhile for a clock radio time backup, or a kitchen scale, but probably worth it for smoke detectors or toy remotes.


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## MidnightDistortions (Dec 31, 2014)

yoyobrotha said:


> I haven't used them in smoke detectors yet, I don't have that level of confidence in them since I haven't done any long term testing with them.



Yeah i haven't tested rechargeables in smoke detectors either, i don't really think it's a good idea but again i just never tested them. You would have to know what voltage sets the low battery indicator and what is the cut off voltage. I couldn't imagine checking it daily either. One suggestion though is to get an extra detector and test the rechargeable with it and see whether they will work. Don't know if they got some that will work with NiMH cells but they are generally designed for alkalines.

As for my experience with 9volt rechargeables, i haven't used them much but after seeing my 9 volt rechargeables sit in storage (checking every month) they still got 8.8volts on them. I only really need them for one of my multimeters and a infrared digital thermometer.


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## UserName (Dec 31, 2014)

I don't get the hesitation to smoke detectors. The general feel of the forum is that everyone trusts their rechargeables so much more than alkalines, but somehow the smoke detector is different? 

I don't see the difference. Instead of replacing the battery when the device chirps the low battery warning, I can recharge it, or replace it with a ready charged spare. 

With rechargeables, you can change out battery with half charge remaining, and have wasted nothing. I could actually follow that suggested *change the batteries when you change the clocks* idea. I think that idea is a conspiracy put forth by battery manufacturers. I check mine at every time change (test voltage, use test button on device, and extinguish a match below the detector), and I routinely get 2 years service from one.


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## WalkIntoTheLight (Dec 31, 2014)

UserName said:


> I don't get the hesitation to smoke detectors. The general feel of the forum is that everyone trusts their rechargeables so much more than alkalines, but somehow the smoke detector is different?
> 
> I don't see the difference. Instead of replacing the battery when the device chirps the low battery warning, I can recharge it, or replace it with a ready charged spare.
> 
> With rechargeables, you can change out battery with half charge remaining, and have wasted nothing. I could actually follow that suggested *change the batteries when you change the clocks* idea. I think that idea is a conspiracy put forth by battery manufacturers. I check mine at every time change (test voltage, use test button on device, and extinguish a match below the detector), and I routinely get 2 years service from one.



Yes, I use rechargeables in my smoke detectors without any problems. Based on when I used to use alkalines in them, they start to chirp low battery warnings when they get down to around 7.5v. A rechargeable 9 volt (8.4v nominal) is going to be fine in them. The only issue may be that you get very little warning when the detector starts to chirp, because a rechargeable 9 volt battery at 7.5v is almost completely empty.

So, just charge them up once or twice a year, and they'll be fine. Whenever I charge mine, I say "SUCK IT" to Duracell.

I don't think I'd use non LSD batteries in smoke detectors, but the LSD ones are fine.


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## Yamabushi (Dec 31, 2014)

Consider carefully before using anything in a smoke detector other that the batteries which are listed in the user manual. The listed models and brands of batteries are the ones with which the model of smoke detector was tested for certification (e.g., Underwriters Laboratories). 

Other batteries would probably work fine but you could run into problems if you file an insurance claim; insurance companies look for excuses to not pay.


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## WalkIntoTheLight (Jan 1, 2015)

Yamabushi said:


> Other batteries would probably work fine but you could run into problems if you file an insurance claim; insurance companies look for excuses to not pay.



Normally, I'd agree with you about insurance companies acting like scum-bags. But, in the case of a smoke detector, I don't see how the battery type would factor into a claim, assuming _the smoke detector works with the battery_. If it goes off, you wake up and leave, and the insurance company can't really argue the battery was faulty. If you have a fire when you're not home, it doesn't matter whether it works or not.

So it's really just a case of whether or not you trust battery types other than alkalines in your smoke detector. (Note that lithium primaries may suffer from the short low-batt warning, since the discharge curves are different.) For the average Joe, he should definitely stick to name-brand alkalines. For those that appreciate different battery chemistries, they should be fine as long as they understand the differences. If you use rechargeables or lithiums, test the detector at least monthly. There's usually a push-button for this.

If you consider overall risks, how many people are still using a smoke detector way past its expiration date? When I bought my last detectors, I think they had an expiration limit of something like 5 years.


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## UserName (Jan 1, 2015)

This is where I wish there was a charger/analyzer like the maha for 9v batts. I could put one in and run it for 6 months, then discharge to see remaining capacity, and get a feel for how long it would run.

My DMMs use up 9v faster than a smoke detector, so I'll probably try them first, both because faster usage equates to battery savings sooner, and because if one lasts a year in one of my meters, it will definitely last that long in a smoke detector.

I still need to determine if I want to try lithium, or LSD NiMH, and then an appropriate charger.

This would be an easy decision of there was an eneloop 9v...


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## UserName (Jan 1, 2015)

Does anyone know what the current draw of an average smoke detector is, anyway?

I'm looking at stuff like energizer's data sheet showing about 600 mAh capacity in their alkaline 9V when discharged at 25mA. I'm thinking a smoke detector is going to draw much less than 25 mA, which is starting to suggest rechargeables would fall short in this very low continuous draw long term usage scenario. My meters, on the other hand will draw nothing when not in use, but substantially more than a smoke alarm when in use. I think I'm going to refocus towards just taking care of my meters, and maybe some garage door openers. Maybe I'll do a test with a secondary smoke alarm, just to get a feel what expected service duration a rechargeable might give, but for the time being, I will continue to rely on alkalines for main ones.


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## WalkIntoTheLight (Jan 1, 2015)

UserName said:


> Does anyone know what the current draw of an average smoke detector is, anyway?



Obviously it depends a lot on the smoke detector. But based on the usage of my latest smoke detectors (a couple of years old), they last about a year on an alkaline, and based on a rough estimate of leftover capacity of a NiMH rechargeable after 2 months, they'd last about 8 months on a 200mAh battery. That would put their drain somewhere around 30uA.

But I've had smoke detectors in the past that lasted far longer than a year on an alkaline, so YMMV. 30uA-40uA is probably an upper limit.

P.S. Keep in mind that on my smoke detectors, they started to sound the low-batt warning about 7.5v, which is when I'd replace the battery. I think on an alkaline this is only about 50% drained. Perhaps they'd still run for a long time after this, but I certainly don't want to listen to them complain about it.


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## MidnightDistortions (Jan 1, 2015)

UserName said:


> I don't get the hesitation to smoke detectors. The general feel of the forum is that everyone trusts their rechargeables so much more than alkalines, but somehow the smoke detector is different?
> 
> I don't see the difference. Instead of replacing the battery when the device chirps the low battery warning, I can recharge it, or replace it with a ready charged spare.
> 
> With rechargeables, you can change out battery with half charge remaining, and have wasted nothing. I could actually follow that suggested *change the batteries when you change the clocks* idea. I think that idea is a conspiracy put forth by battery manufacturers. I check mine at every time change (test voltage, use test button on device, and extinguish a match below the detector), and I routinely get 2 years service from one.





WalkIntoTheLight said:


> Yes, I use rechargeables in my smoke detectors without any problems. Based on when I used to use alkalines in them, they start to chirp low battery warnings when they get down to around 7.5v. A rechargeable 9 volt (8.4v nominal) is going to be fine in them. The only issue may be that you get very little warning when the detector starts to chirp, because a rechargeable 9 volt battery at 7.5v is almost completely empty.
> 
> So, just charge them up once or twice a year, and they'll be fine. Whenever I charge mine, I say "SUCK IT" to Duracell.
> 
> I don't think I'd use non LSD batteries in smoke detectors, but the LSD ones are fine.




I don't use rechargeables mostly because i live in an apartment and there's always a chance i'd lose those batteries. I prefer having new cells in the device versus using one that has lost capacity or is old. A fresh alkaline is cheaper and i don't have to worry about it.


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## WalkIntoTheLight (Jan 1, 2015)

MidnightDistortions said:


> I don't use rechargeables mostly because i live in an apartment and there's always a chance i'd lose those batteries. I prefer having new cells in the device versus using one that has lost capacity or is old. A fresh alkaline is cheaper and i don't have to worry about it.



Yes, I really don't have a lot of 9 volt rechargeable batteries (compared to my too-big AA and AAA collection), because I find 9v alkalines don't leak very often, and they are a lot cheaper.


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## NoNotAgain (Jan 1, 2015)

A lot of states have changed their fire code regulations to require 10 year lithium primaries only. 

As for in the past and using alkaleaks, if you follow the recommend replacement of changing out cells when you go from standard time to day light savings time and back, just makes sense. 

Each year the fire department goes around giving out new smoke detectors after the first indigent family burns up due to a non working detector. 

Spend the $4.00 a year to replace the batteries or get one of the lithium powered units.


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## Yamabushi (Jan 1, 2015)

WalkIntoTheLight said:


> ... But, in the case of a smoke detector, I don't see how the battery type would factor into a claim, assuming _the smoke detector works with the battery_. If it goes off, you wake up and leave, and the insurance company can't really argue the battery was faulty. If you have a fire when you're not home, it doesn't matter whether it works or not. ...


Some of us receive a discount on our insurance premium based on monitored smoke detectors. These are usually wired with backup battery power from the alarm panel but some are wireless and depend on a battery for both the detector and RF connectivity to the alarm panel.


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## WalkIntoTheLight (Jan 1, 2015)

Yamabushi said:


> Some of us receive a discount on our insurance premium based on monitored smoke detectors. These are usually wired with backup battery power from the alarm panel but some are wireless and depend on a battery for both the detector and RF connectivity to the alarm panel.



Okay, but if they are monitored, doesn't the monitor panel tell you when the batteries are low/dead?

I think the biggest advantage of alkalines is for people that are too lazy to change their smoke detector batteries (which is most people). They also have a very slow and large voltage drop-off, so they will run long after the detectors start to annoy you to replace them.

But if you're on a schedule to replace batteries, I don't see the harm in using rechargeables. They certainly work. It's just a matter of being bothered to recharge them.


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## UserName (Jan 1, 2015)

I didn't know about the 10 year lithiums when I started this thread. I'm still going to pick out a rechargeable 9v system for my other stuff, and I may stick a spare battery in an extra detector just to satisfy my own curiosity what happens. When they can make a battery that lasts 10 years it really takes the wastefulness out of the disposable battery concept (isn't it recommended to replace smoke detectors on 10 year intervals anyway?)


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## WalkIntoTheLight (Jan 1, 2015)

UserName said:


> I didn't know about the 10 year lithiums when I started this thread. I'm still going to pick out a rechargeable 9v system for my other stuff, and I may stick a spare battery in an extra detector just to satisfy my own curiosity what happens. When they can make a battery that lasts 10 years it really takes the wastefulness out of the disposable battery concept (isn't it recommended to replace smoke detectors on 10 year intervals anyway?)



I think the 10 years for lithiums is its _shelf life_, not necessarily its operating life. Alkalines (9 volt) shelf life is 5 years, but I wouldn't recommend only changing your smoke detector batteries every 5 years whether they're alkalines or lithiums. Lithiums will have greater capacity than alkalines, but not several times more.


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## UserName (Jan 1, 2015)

It seems to go either way. It can be a 9V style of battery with a 10 year *warranty*. I doubt this one would last that long.

It can also be a smoke detector with a non-replaceable lithium battery guaranteed to last 10 years.


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## MidnightDistortions (Jan 1, 2015)

WalkIntoTheLight said:


> Yes, I really don't have a lot of 9 volt rechargeable batteries (compared to my too-big AA and AAA collection), because I find 9v alkalines don't leak very often, and they are a lot cheaper.



I got 2 9 volt rechargeable batteries with Tenergy, i was planning to put one in a multimeter and the other in my infrared thermometer. With that being said i don't mind spending money on some alkalines for smoke detectors. At least until i get my own smoke detector.


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## WalkIntoTheLight (Jan 2, 2015)

MidnightDistortions said:


> I got 2 9 volt rechargeable batteries with Tenergy, i was planning to put one in a multimeter and the other in my infrared thermometer. With that being said i don't mind spending money on some alkalines for smoke detectors. At least until i get my own smoke detector.



I'm now running a test to see how rechargeable 9 volt batteries perform in smoke detectors. I charged up two batteries, a Tenergy Centura 200mAh LSD 9v, and an Energizer 175mAh 9v (non LSD). Both of these batteries are new. I've put them in two identical smoke detectors. These detectors are occasionally triggered accidentally once or twice a week (usually from cooking), so they're not completely idle.

I'll report back when the smoke detectors start to issue a warning chirp. I'm not sure if I'll continue after that, because it's very annoying.

I may report back once in awhile to give the current voltage of the batteries, to see how they're holding up. Starting voltages on these batteries are both around 9.2v-9.3v.


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## Epsilon (Jan 2, 2015)

WalkIntoTheLight said:


> I think the 10 years for lithiums is its _shelf life_, not necessarily its operating life. Alkalines (9 volt) shelf life is 5 years, but I wouldn't recommend only changing your smoke detector batteries every 5 years whether they're alkalines or lithiums. Lithiums will have greater capacity than alkalines, but not several times more.


Are there no smoke detectors running on 3*CR123 batteries? They are a little bigger than 9v alkalines, but with 1500mAh about 8 times the capacity.


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## Tobias Bossert (Jan 2, 2015)

Primary lithium 9V-blocks (6LR61) provide about 1200mAh. They have a neglectible self discharge rate: after 10 years without load they guarantee at least 85% of charge. They start at prices of about 5$ per piece. Why not using them?


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## Illum (Jan 2, 2015)

Tobias Bossert said:


> Primary lithium 9V-blocks (6LR61) provide about 1200mAh. They have a neglectible self discharge rate: after 10 years without load they guarantee at least 85% of charge. They start at prices of about 5$ per piece. Why not using them?




err.... 6LR61 [or ANSI-1604A, IEC-6LR61] designates it a Alkaline-Manganese Dioxide Battery or of Zinc-Manganese Dioxide (Zn/MnO2) chemistry. Primary Lithium has a different name, [ANSI-1604LC] 

---

Honestly, I have not bought one that didn't arrive flat or almost flat, and I've tested my luck with ultralife [bought about 6-7 over the years] till my patience ran out. I have not been able to locate a reliable source for these "1200mAH" 9V batteries. The batteries I received from Ultralife has almost always been DOA. zero volts, packaged in U9VL-X packaging with expiration dates of 2019 and 2020, marked U9VL-J.

Now Energizer advanced lithium only sports 750mAH, but they do it pretty consistently. 
http://data.energizer.com/PDFs/la522.pdf


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## WalkIntoTheLight (Jan 2, 2015)

Illum said:


> Now Energizer advanced lithium only sports 750mAH, but they do it pretty consistently.



Where I live, they cost 4x the price of alkaline 9 volts. I'm just not sure the cost/benefit is worth it, considering they certainly don't have 4x the capacity. (This is also the case with AA lithium primaries. It's just expensive to buy them in Canada.)

I suppose if you have a really expensive device that runs on 9 volts, and you don't want to use NiMH or risk an alkaline leaking, then maybe it's worth going with lithium primaries. Or, if the device needs to perform well in very cold conditions. But for me, they're just too expensive for a throw-away battery.


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## MidnightDistortions (Jan 2, 2015)

WalkIntoTheLight said:


> I'm now running a test to see how rechargeable 9 volt batteries perform in smoke detectors. I charged up two batteries, a Tenergy Centura 200mAh LSD 9v, and an Energizer 175mAh 9v (non LSD). Both of these batteries are new. I've put them in two identical smoke detectors. These detectors are occasionally triggered accidentally once or twice a week (usually from cooking), so they're not completely idle.
> 
> I'll report back when the smoke detectors start to issue a warning chirp. I'm not sure if I'll continue after that, because it's very annoying.
> 
> I may report back once in awhile to give the current voltage of the batteries, to see how they're holding up. Starting voltages on these batteries are both around 9.2v-9.3v.



Yeah those warning chirps are annoying. Maybe stick it under a pillow in the garage or basement so you can hear it when you are in the room but it won't drive everyone nuts lol.


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## Epsilon (Jan 2, 2015)

Tobias Bossert said:


> Primary lithium 9V-blocks (6LR61) provide about 1200mAh. They have a neglectible self discharge rate: after 10 years without load they guarantee at least 85% of charge. They start at prices of about 5$ per piece. Why not using them?


Wow, didn't know that they are such a leap forward fs alkaline.


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## InHisName (Jan 13, 2015)

I investigated using 8.4v and 9.6v rechargeables for our church microphones. Alkalines lasted 3+ sundays. The 9.6 couldn't quite last that thrid sunday when the low battery light showed. Replaced and recharged. cycle and rinsed three times and the batteries were totally useless.Tried 8.4v and they lasted 3 sundays. But we kept forgetting and low battery showed 4th sunday. So we replaced and recharged. Got 5-6 cycles before permently dead. 

So then I investigated with a dead Alkaline. 7.1v open circuit. Measured 5.9v with mic on. After 8 minutes low batt came on. it was 5.56v. Now I see why these died so early. The 9.6v ones must have had SEVERAL cells being reversed charged EACH cycle! Even the 8.4v must have had at least 2 cells reverse cycling each time. 

I looked for a 7.2v NiMH and found almost none! I ordered one from unknown china source and waited 43 days. It charged to about 8.2v but in mic settled to 7.5v very quick. It did last over 4 sundays before the low batt light. I suspect even with this one a cell was probably being reversed charged. I proposed we order a bunch of these and rechard 2x month. Got overruled the rest of comittee would rather spend $9-11 on Lithiums and toss when low batt lightsup. They do last 6-7 sundays though.

I figured the chinese 7.2v would cycle at least 20x where we might go 2 or 3 sundays max each cycle. So that means at least 40 sundays total before gone for only $3 each. Sure seemed better than 7 sundays for $11.

If a smoke alarm beeps at 7.5 v, then there is hope an 8.4v might not get ruined too fast. It a smoke alarm beeps at 5.5v or so then none of the NiMH batteries would last very long.


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## UserName (Jan 13, 2015)

That is a good point. 

I've abandoned the idea of using these in smoke alarms, in favor of the longest lasting lithium primary I can substitute.

I'm still looking at the possibility of using them in my multimeters. I may be better off looking at a lithium ion type rechargable. I should be able to count on it's protection circuit cutting off the battery when sufficiently discharged, right?

On my meters, often when the battery indicator comes on, I make sure I have spares in the toolbox, but then continue to use that battery until the meter no longer functions, or gives me reason to question it's accuracy. Batteries have tested in the just over 6 volts range when removed. With NiMH cells in series, I would hazard a guess it is best to not discharge below 1 volt/cell. A 7 cell 8.4 volt battery would be at .86 volts/cell, while an 8 cell 9.6 volt battery would be at .75 volts/cell. What is the standard for discharging a NiMH battery pack? Is it recommended to terminate discharge at a point of x volts per cell?

I may need to either make a habit of recharging more frequently, or look into a lithium based rechargeable solution. In that case, I should be able to count on the protection circuit of the battery to cut it off before overdischarge, right?


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## WalkIntoTheLight (Jan 13, 2015)

InHisName said:


> So then I investigated with a dead Alkaline. 7.1v open circuit. Measured 5.9v with mic on. After 8 minutes low batt came on. it was 5.56v. Now I see why these died so early. The 9.6v ones must have had SEVERAL cells being reversed charged EACH cycle! Even the 8.4v must have had at least 2 cells reverse cycling each time.



Why do you assume reverse-charging is going on? 5.56v / 7 = 0.79v per cell. Okay, I'll grant you that implies the cells are pretty-much empty, and that some may be more empty than others.

But in my tests of multi-cell lights (with somewhat mismatched cells), I find that as one cell approaches 0 volts, even if others are still around 1.2 volts, the current is almost shut down completely. It seems that the empty cell's internal resistance rises to a point where it becomes more and more difficult for current to flow through the battery, making reverse-charging more and more difficult.

I'm sure if I left it that way for long enough, the bad cell would become reverse-charged (and I've seen it happen), but if you take the battery out soon after you get your low-voltage warning, shouldn't that prevent reverse-charging?

Perhaps the quality of the 9v battery is at fault, not necessarily reverse-charging that would affect all batteries? What brand were you using? Even with damage caused by some reverse charging, I'd expect they'd last more than 3 charges. How were you charging them? Could that be part of the problem?

When I've taken apart dead 9v NiMH batteries and measured the cells, it does appear to be the fault of 1 cell that dies before the others. But these were old batteries, so I'm not sure if it was reverse-charging that caused the death.


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## more_vampires (Jan 13, 2015)

+1 for lithium primaries in low draw devices such as smoke alarms. About 2 years ago I went around replacing dead alkaleaks with no-leak Energizer lithium primaries. I've not replaced any yet from the annoying low voltage chirp.

On the packaging, they gush a lot about how great they are as a backup battery for an otherwise powered smoke alarm unit. ...that it could possibly last up to 10 years like that. Maybe, maybe not: marketing.

Over half the time when I replace a smoke alarm battery that was alkaline... it leaked! I have to walk around with a pink pencil eraser to clean contacts during the battery swap.

...plus, the Energizer silvery sleeve looks darned cool when hooked to a Paklite!  Possibly the sexiest 9 volt battery out there. :laughing:

Not a fan of 9v rechargeable for some strange reason. Don't know why...


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## ChrisGarrett (Jan 13, 2015)

Doing fine after two plus years with Tenergy's two bay smart charger and four Centuras. I don't use them in critical items, only: alarm clock backup, a SPL meter and an AM/FM radio.

Chris


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## MidnightDistortions (Jan 13, 2015)

InHisName said:


> I investigated using 8.4v and 9.6v rechargeables for our church microphones. Alkalines lasted 3+ sundays. The 9.6 couldn't quite last that thrid sunday when the low battery light showed. Replaced and recharged. cycle and rinsed three times and the batteries were totally useless.Tried 8.4v and they lasted 3 sundays. But we kept forgetting and low battery showed 4th sunday. So we replaced and recharged. Got 5-6 cycles before permently dead.
> 
> So then I investigated with a dead Alkaline. 7.1v open circuit. Measured 5.9v with mic on. After 8 minutes low batt came on. it was 5.56v. Now I see why these died so early. The 9.6v ones must have had SEVERAL cells being reversed charged EACH cycle! Even the 8.4v must have had at least 2 cells reverse cycling each time.
> 
> ...



Which brand are these batteries that only lasted a few cycles? Charger? It might be possible that these batteries were no good or the charger overcharged the batteries (or undercharged them).




WalkIntoTheLight said:


> Why do you assume reverse-charging is going on? 5.56v / 7 = 0.79v per cell. Okay, I'll grant you that implies the cells are pretty-much empty, and that some may be more empty than others.
> 
> But in my tests of multi-cell lights (with somewhat mismatched cells), I find that as one cell approaches 0 volts, even if others are still around 1.2 volts, the current is almost shut down completely. It seems that the empty cell's internal resistance rises to a point where it becomes more and more difficult for current to flow through the battery, making reverse-charging more and more difficult.
> 
> ...




I have been told that 3-4 volts for a NiMH 9v cell is ideal though i have accidently dropped it down to 2 volts. The Tenergys still hold a charge even after several months. I vote for the quality of the battery being bad as well. It might be well possible that InHisName got a bad set of 9 volts. I might run some more tests to confirm whether 9 volts prematurely die after a few cycles but i think it's the battery or the charger. I don't have that much experience with 9 volts here but i'm questioning the quality of the charger/batteries before questioning whether the mic is overdischarging the battery. There's another factor, since 9 volt batteries is basically a pack of AAAA (i think that's right?) batteries and if the device is incorrectly drawing or the connection on the terminals is bad (this most likely would lead back to the battery itself) it might draw more power from one battery than the rest effectively killing the 9v. It could also mean that one of the batteries is not properly connected in the battery itself. I've seen more than my fare share of poorly connected batteries that more often fail or exhibit problems down the road.


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## more_vampires (Jan 13, 2015)

MidnightDistortions said:


> There's another factor, since 9 volt batteries is basically a pack of AAAA (i think that's right?) batteries



Yeah, but not always. It's like how you can tear open "6 volt lantern batteries" and find D or AA cells sometimes (and sometimes you just ruin a solid battery.)

I hear Reppans does it all the time!


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## WalkIntoTheLight (Jan 13, 2015)

MidnightDistortions said:


> There's another factor, since 9 volt batteries is basically a pack of AAAA (i think that's right?) batteries and if the device is incorrectly drawing or the connection on the terminals is bad (this most likely would lead back to the battery itself) it might draw more power from one battery than the rest effectively killing the 9v. It could also mean that one of the batteries is not properly connected in the battery itself. I've seen more than my fare share of poorly connected batteries that more often fail or exhibit problems down the road.



I think you'd notice that in the battery voltage, right from the start. The NiMH 9 volts I've torn apart all had soldered tabs holding the AAAA's together in series. I don't think one cell could drain faster than any other cell, using that construction. If they soldered them wrong, the voltage wouldn't be right.





more_vampires said:


> Yeah, but not always. It's like how you can tear open "6 volt lantern batteries" and find D or AA cells sometimes (and sometimes you just ruin a solid battery.)



I think all the 9 volt NiMH batteries are constructed from AAAA sized cells, but I could be wrong. The major name-brand alkaline 9 volts are built that way too (but only 6 of them, unlike the 7 or 8 you find in NiMH). The carbon-zinc 9 volts are built from 6 small rectangular cells stacked on top of each other.

I'm not sure why some are different than others. Perhaps it's easier to manufacture alkaline cells as cylinders?

The big 6 volt batteries usually have "long" D cells in them. I haven't ever seen AA's inside of them.


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## Kurt_Woloch (Jan 13, 2015)

I'll go with the thread topic here... my experiences with 9V rechargeables:

My first one was a SAFT 75 mAh NiCd 9V battery. I got this before I even had a suitable charger for it, hence it didn't get much use. I don't remember how I charged it. My 9V appliances kept changing anyway, but in April 1987 I bought a multimeter that ran on a 9V, so this rechargeable one was put in that DMM. Must have been this way since I can't remember ever having used disposable batteries in it, and at that time I definitely didn't have any other rechargeable 9V's, though it might be that originally I had two of the SAFT's, not one... but it's been to long to remember for sure.

Then we bought 2 more in 1989. They were white from the unknown brand "Jewo", supposedly made in Japan. Can't remember what their purpose was, but they had a higher capacity of 100 mAh each, at 8,4V. If I had 2 SAFT, then this must have happened after the first of those got bad.

In 1992 I bought a delay effect pedal which works on a 9V, and it turned out it actually ran better on the SAFT than on the JEWO's because those were some type of NiCd battery (I think non-sintered) having a pretty high internal resistance, and the pedal draws up to 55 mA, so at that load the JEWO's gave a lower voltage than the SAFT, which seems to have been a sintered-cell model. However, the JEWO's also had a pretty low self discharge, so the multimeter worked for months on a charge.

In 1993 I bought a UCAR 9V with 110 mAh which was very similar to the JEWO's and also had that high internal resistance. Back then I figured you just can't get better rechargeable 9V's, but I still kept on using them in the DMM, and then in a digital bathroom scale I got in 2004 and a phantom power unit for a headset I got in 1999. By then one of the JEWO's had given up, but the other and the UCAR still were alive. In fact, those two are still here. The UCAR, however, is about to be recycled since at least one cell of it seems to have given up after I tested it two years ago (apparently too hard) and its case is cracked, but the JEWO, although it's now over 25 years old, at least still has full voltage, although its capacity has shrunk to 30 mAh if I remember right. It would still be able to power the DMM or the scale though, but...

in the last three years I bought three new NiMh 9V's in total, but I lost one of them due to an accidental short-circuit in my bag. Those now give a reasonable amount of power at an internal resistance which in any case is lower than that of a new Alkaline 9V. One of them is a 200 mAh Varta which was sold "ready to use", the other one a 250 mAh from ActivEnergy (house brand of discount chain Aldi / Hofer). They now power the digital scale and one of the DMM's (one which actually has been replaced by another one I got for Christmas which takes 2 AAA's). There they give a better runtime than them old NiCd's.

Except for the NiCd ones not sufficiently being able to power that pedal, I had few problems with them in the last 25 years. I just recharged them whenever they got empty, and they kept on going and going and going... I don't have a smoke detector so I don't have any preferences what batteries should be used there. In fact, I think the 9V's are the only size where I don't even have disposable batteries laying around, or at least ones that are not "crap". ;-)


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## MidnightDistortions (Jan 13, 2015)

WalkIntoTheLight said:


> I think you'd notice that in the battery voltage, right from the start. The NiMH 9 volts I've torn apart all had soldered tabs holding the AAAA's together in series. I don't think one cell could drain faster than any other cell, using that construction. If they soldered them wrong, the voltage wouldn't be right.



Well, i'm going for the bad charger theory then and/or that the 9 volt batteries are a cheap brand that wasn't properly manufactured and it's some kind of defect.


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## UserName (Jan 16, 2015)

Thanks to everyone that offered input.

After rereading the thread again, and thinking on it a little while longer, I've determined I don't think I can benefit from rechargeable 9V's at this time. If something better comes out, or they get cheaper, or my usage increases, that will change things. Meanwhile, the dozen pack of duracell procell 9v batteries I can get online for $14 will last me at minimum a year and a half, at most 2 years. I just don't use enough to justify anything else right now.


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## WalkIntoTheLight (Mar 20, 2015)

WalkIntoTheLight said:


> I'm now running a test to see how rechargeable 9 volt batteries perform in smoke detectors. I charged up two batteries, a Tenergy Centura 200mAh LSD 9v, and an Energizer 175mAh 9v (non LSD). Both of these batteries are new. I've put them in two identical smoke detectors. These detectors are occasionally triggered accidentally once or twice a week (usually from cooking), so they're not completely idle.
> 
> I'll report back when the smoke detectors start to issue a warning chirp. I'm not sure if I'll continue after that, because it's very annoying.
> 
> I may report back once in awhile to give the current voltage of the batteries, to see how they're holding up. Starting voltages on these batteries are both around 9.2v-9.3v.



This is an update after 80 days in use. Both the Tenergy Centura and the Energizer Recharge are holding up well. Each smoke detector is triggered about twice a week. They are rotated weekly to ensure they are exposed to the same conditions.

Here are the resting voltages after 80 days:

- An unused Tenergy Centura (LSD, claims 85% charge after 1 year, 70% after 2 years): currently 9.13v
- The used Tenergy Centura: 8.91v
- The used Energizer Recharge: 8.90v

I'm a little surprised the Energizer is so close in voltage to the Tenergy. The Energizer is 175mAh, and is not low-self-discharge. However, it compares almost exactly to the Tenergy Centura, a 200mAh low-self-discharge battery. Both batteries are 7-cell NiMH rechargeables (nominal 8.4v). Perhaps the self-discharge of the Energizer will accelerate in the next few months, or maybe it's very similar in construction to the Tenergy Centura.

From earlier testing, I estimate a "full" charge is about 9.2v, after resting a few weeks. They initially charge to about 10.1v, but this drops rapidly. When they get down to about 9.2v, the drop is very slow. (Yes, I know voltage alone can't be used for an accurate determination of capacity, but it's a good-enough method for this test.)

If 8.4v indicates almost empty (which is 1.2v per cell), and 9.2v indicates full, then I can estimate current capacity.

Both used batteries are about 62% full. The unused battery is about 91% full. Of course, these are only estimates.

The 62% full seems to be as expected, based on how these smoke detectors eat alkaline batteries. Alkalines last about a year, and they have more capacity. These rechargeable 9 volts are on track to be dead after about 7 months use, based on current estimates. We'll see.


So far, I'm pleased with using rechargeable 9 volt batteries in smoke detectors. It does save money, compared to alkalines, assuming they'll last at least 4 years (which they should easily). You do have to be sure to charge them, and test your smoke detector regularly, or they could run down without notice. Although I think they'll last over 6 months between charges, I'd recommend charging them every 3 or 4 months, just to be safe.


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## WalkIntoTheLight (May 15, 2015)

Here are the resting voltages after 135 days in smoke detectors:

- An unused Tenergy Centura (LSD, claims 85% charge after 1 year, 70% after 2 years): currently 9.08v
- The used Tenergy Centura: 8.81v
- The used Energizer Recharge: 8.79v

Not much drop in the past 55 days, only about -0.1 volts. Both the low-self-discharge and regular NiMH battery are doing about the same. The unused battery dropped only -0.05v in the past 55 days.

They are 7-cell batteries, so each cell (in the used batteries) is a little less than 1.26v. A little less than half capacity left after 4.5 months? My hope is that they will last at least 7 months, so I only need to charge them up a couple of times per year.


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## NoNotAgain (May 16, 2015)

Home Depot sells a smoke detector manufactured by Code One that uses a sealed in place lithium Ion battery that they warranty to still be functional for 10 years.

Quite a few municipalities are changing their fire code regulations to require this type of detector ONLY.

A lot of cities with high populations of poor people used to hand out smoke detectors every year. The fire department would come back the following year to find that either the detector was chirping or the batteries were removed. 

I personally like the sealed in battery approach and toss the unit at 10 years. The ionizer is usually toast anyway and the manufacturers recommend replacement anyway.


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## WalkIntoTheLight (May 16, 2015)

NoNotAgain said:


> Home Depot sells a smoke detector manufactured by Code One that uses a sealed in place lithium Ion battery that they warranty to still be functional for 10 years.



It must be a very efficient smoke detector. In my detectors (the ones I'm testing), alkalines would be almost drained after about a year. Lithiums don't have 10x the capacity of alkalines. Maybe double?

(I doubt they're lithium ions being used, they're likely lithium primaries.)


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## NoNotAgain (May 16, 2015)

WalkIntoTheLight said:


> It must be a very efficient smoke detector. In my detectors (the ones I'm testing), alkalines would be almost drained after about a year. Lithiums don't have 10x the capacity of alkalines. Maybe double?
> 
> (I doubt they're lithium ions being used, they're likely lithium primaries.)



Direct quote from the Home Depot description. 

"10-Year Lithium Ion Battery Operated Ionization Smoke Alarm"

http://t.homedepot.com/p/Code-One-1...ted-Ionization-Smoke-Alarm-21009992/203728679


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## WalkIntoTheLight (May 16, 2015)

NoNotAgain said:


> Direct quote from the Home Depot description.
> 
> "10-Year Lithium Ion Battery Operated Ionization Smoke Alarm"
> 
> http://t.homedepot.com/p/Code-One-1...ted-Ionization-Smoke-Alarm-21009992/203728679



Well, I still don't think they're using a lithium-ion battery. That doesn't make much sense for a long-duration throw-away device. Lithium primary makes a whole lot more sense. Probably a mistake in Home Depot's listing.


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## SaraAB87 (May 17, 2015)

I am sure that my alkalines last more than a year in the smoke detectors at least. They are just off the shelf duracells, energizers and ray o vac. I have never had a leak.

Usually when the detector starts beeping we find the alkaline in there has an expired date.

We have a guy who comes every year and checks the smoke detectors, provided by the city since we have an elderly person in the house.

The thermostat is another story, they recommend changing it every year, it's only 2 alkaline AA's so it's cheap to maintain. I am sure those batteries in there would last a long time, but it seems to be more voltage sensitive than other stuff so it needs to be replaced at least once a year.


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## WalkIntoTheLight (May 18, 2015)

SaraAB87 said:


> I am sure that my alkalines last more than a year in the smoke detectors at least. They are just off the shelf duracells, energizers and ray o vac. I have never had a leak.



Yes, most smoke detectors last well over a year on alkalines. The ones I'm testing just seem to be very inefficient (cheap ones bought at Costco), which is good for testing because I won't have to wait several years for the results. But yes, the ones I'm using really are abnormally inefficient.



> The thermostat is another story, they recommend changing it every year, it's only 2 alkaline AA's so it's cheap to maintain. I am sure those batteries in there would last a long time, but it seems to be more voltage sensitive than other stuff so it needs to be replaced at least once a year.



I use Eneloops in my furnace thermostat. I charge them once a year, and they still have about two-thirds their capacity left.

I think every manufacturer of smoke detectors, thermostat controls, etc., all say to change the batteries once or twice a year. It's CYA stuff. If the batteries suck or you forget for a couple of years, it'll still work.


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## TinderBox (UK) (May 18, 2015)

What is the highest real capacity low discharge/pre charged 9V battery , I have a couple of Vapex instant 200mah 9v and they seem to work fine.

I would not trust ni-mh 9v battery`s in a smoke alarm as rechargeable battery can suddenly go flat and you might miss the low battery warning, if you are out, I much prefer Alkaline or Linthium , both have approx the came capacity, but Alkaline chokes under high loads and you only get a percentage of the capacity, when lithium works much better and will last longer, but only in high drain appliances.

I have mains powered smoke alarms in my home, they have an lithium backup battery in case of power failure.

John.


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## MidnightDistortions (May 18, 2015)

The only problem i have with 9V cells now is that there are not many chargers out there for them to test their capacity and so far i just have the Tenurgy kit. One option for 9V NiMH's is to replace the cell every 3 years with a fresh one. I don't trust the built in lithium ones. They could die before the unit goes bad and you'll just be throwing away a perfectly good unit. I'd rather have a user replaceable battery along with a user replaceable ionizer so you can keep the unit and replace the non functioning part.


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## WalkIntoTheLight (May 18, 2015)

MidnightDistortions said:


> One option for 9V NiMH's is to replace the cell every 3 years with a fresh one.



That's fine if you're using them in moderate-drain devices and charging them several times per year, you still get your money's worth. But NiMH 9v costs about 4x more than a quality alkaline. For a smoke detector, you'd better get many years out of a NiMH 9v, or it's more cost-effective to just use alkalines.


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## WalkIntoTheLight (Jun 29, 2015)

Time for the 6-month update on the use of 9v NiMH rechargeables in smoke detectors:

- An unused Tenergy Centura (LSD, claims 85% charge after 1 year, 70% after 2 years): currently 9.05v
- The used Tenergy Centura: 8.77v
- The used Energizer Recharge: 8.78v

Very little voltage drop in all samples since I last checked 1.5 months ago. Both the low-self-discharge and regular NiMH battery are doing the same. I'm not sure if the Tenergy Centura really does retain 85% charge after 1 year, since I doubt the unused battery still has that much in it after just 6 months, but I have no way to know for sure. OTOH, the Energizer, which doesn't claim to be LSD, seems to be holding up just as well as the Tenergy.


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## Kurt_Woloch (Jun 29, 2015)

I've also done some self-discharge tests in the last months (mostly on AA batteries though). From your tests so far, the unused Tenergy battery still has a higher voltage now after 6 months than the used one had after 80 days. If the unused battery keeps dropping at the same rate it did in the last 45 days, it will take another 7 months to reach 8,91v, at which point it will have self-discharged to the level the used battery reached after 2 months. We don't know how many mAh this corresponds to /we probably won't find out until the first used battery is depleted), but if the self-discharge takes 13 months to get to the same point as the regular discharge in 2 months (chances are it will actually slow down further), this would mean that the self-discharge is about 15% of it and the regular discharge combined. How much the actual self-discharge level will be is yet to be determined... I'd propose that if the used batteries get depleted, the unused one should continue to sit until it reaches 8,91 V on its own so we at least know how long this takes.

Your batteries are already holding up for a unusual long time (50% of the runtime of an alkaline although they have maybe 35-40% of its capacity), and it doesn't seem like they reach their end yet.


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## WalkIntoTheLight (Jun 29, 2015)

Kurt_Woloch said:


> I've also done some self-discharge tests in the last months (mostly on AA batteries though). From your tests so far, the unused Tenergy battery still has a higher voltage now after 6 months than the used one had after 80 days. If the unused battery keeps dropping at the same rate it did in the last 45 days, it will take another 7 months to reach 8,91v, at which point it will have self-discharged to the level the used battery reached after 2 months. We don't know how many mAh this corresponds to /we probably won't find out until the first used battery is depleted), but if the self-discharge takes 13 months to get to the same point as the regular discharge in 2 months (chances are it will actually slow down further), this would mean that the self-discharge is about 15% of it and the regular discharge combined. How much the actual self-discharge level will be is yet to be determined... I'd propose that if the used batteries get depleted, the unused one should continue to sit until it reaches 8,91 V on its own so we at least know how long this takes.



Yes, I'll try that. I have no way to determine actual capacity or relative capacity of 9v batteries, since I don't own any device that can discharge at a fixed constant rate in a reasonable amount of time.



> Your batteries are already holding up for a unusual long time (50% of the runtime of an alkaline although they have maybe 35-40% of its capacity), and it doesn't seem like they reach their end yet.



Yes, what surprised me most is how little the voltage has dropped on all batteries in the past 1.5 months. It's really started to plateau. They are holding up pretty well compared to my past experience with alkalines, however, those alkalines were probably not fresh, as I tend to buy in bulk and I think they may have sat around a few years before I used them. So, perhaps it isn't a fair comparison.


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## WalkIntoTheLight (Aug 31, 2015)

Time for the 8-month update on the use of 9 volt NiMH rechargeables in smoke detectors:


- An unused Tenergy Centura (LSD, claims 85% charge after 1 year, 70% after 2 years): currently 9.00v
- The used Tenergy Centura: 8.77v
- The used Energizer Recharge: 8.74v

The change in voltage over the past 2 months is almost nil. I'm beginning to wonder if estimating charge using voltage is much use at all. I know it's not too accurate even in good single NiMH cells, but I thought I'd be seeing a steadier voltage drop in these 9 volt NiMH batteries over the past few months.

If I estimate charge based on voltage, full charge should be about 9.24v (1.32v per cell), and empty about 8.40v (1.20v per cell). But it seems these batteries lose voltage more quickly at first, and then very slowly later. So, I'm not sure what the discharge curve looks like.

In any case, they seem to still be working fine; the smoke detectors are triggered about once a week.


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## Rick NJ (Aug 31, 2015)

I did a review of the *Tenergy Centura 9V and TN141 (charger) mini review*. It is not a comprehensive review but it still has info that you may find useful.

I do not have long term voltage info in my review, but I have some detail about discharge characteristics and energy delivery characteristics graph there.

You can see it here:
http://www.eevblog.com/forum/reviews/tenergy-centura-9v-and-tn141-mini-review/


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## WalkIntoTheLight (Aug 31, 2015)

Rick NJ said:


> I do not have long term voltage info in my review, but I have some detail about discharge characteristics and energy delivery characteristics graph there.



Thanks. Your slow discharge graphs explains why the voltage on my batteries has been hanging around the 8.7v level for so long.


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