Please share your experiences with rechargeable 9v batteries.

[WalkIntoTheLight]

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.

 

[Epsilon]

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.

 

[Tobias Bossert]

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?

 

[Illum]

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

 

[WalkIntoTheLight]

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.

 

[MidnightDistortions]

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.

 

[Epsilon]

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.

 

[InHisName]

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.

 

[UserName]

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?

 

[WalkIntoTheLight]

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.

 

[more_vampires]

+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...

 

[ChrisGarrett]

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

 

[MidnightDistortions]

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.

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).

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.

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.

 

[more_vampires]

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!

 

[WalkIntoTheLight]

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.

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.

 

[Kurt_Woloch]

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". ;-)

 

[MidnightDistortions]

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.

 

[UserName]

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.

 

[WalkIntoTheLight]

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.

 

[WalkIntoTheLight]

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.