Reconditioning NiMH batteries? - Page 1
Forum section: electronics / beginners

author: Connecteur
author_rank: Frequent Contributor
timestamp: January 02, 2022, 07:48:54 pm
content: I have a Logitech s-00116 bluetooth speaker with a NiMH battery pack that dates back to 2009 (about 12 years old). It didn't take a charge at first, but the charging indicator was blinking. Today, after leaving it to charge for 2 days, it held enough charge to run the bluetooth speaker for about 15 minutes.If I keep deep-cycling the battery will the charge capacity keep improving? I don't want to bring it back to the original 6-hour run-time, just something reasonable until the new battery pack I ordered arrives.

author: tszaboo
author_rank: Super Contributor
timestamp: January 02, 2022, 08:01:23 pm
content: Check individual cells, maybe they are out of balance.

author: IanB
author_rank: Super Contributor
timestamp: January 02, 2022, 08:03:16 pm
content: You can potentially recondition NiMH batteries by giving them a slow charge for a long time (e.g. 0.1C for 16 hours or so). How well this might work will be variable, and will depend on how far gone the batteries are.

author: Connecteur
author_rank: Frequent Contributor
timestamp: January 02, 2022, 08:04:33 pm
content: Quote from: tszaboo on January 02, 2022, 08:01:23 pmI can do that, but wouldn't a complete discharge put them back in balance?

author: bdunham7
author_rank: Super Contributor
timestamp: January 02, 2022, 08:30:15 pm
content: Quote from: Connecteur on January 02, 2022, 08:04:33 pmNo, if your battery pack is marginal you want to avoid complete discharge because you typically have cell reversal at that point. A very long float charge followed by minimal use and frequent recharging at a low level would be the way to limp it along until you get a new pack.

author: Connecteur
author_rank: Frequent Contributor
timestamp: January 02, 2022, 08:49:35 pm
content: Quote from: bdunham7 on January 02, 2022, 08:30:15 pmIt cuts out when the battery gets low, but I don't know the voltage. The indicator is supposed to turn from green to amber when 2 hours battery are left and then red when 20 minutes are left. It never changed color; it went from green to off. I'm continuing to charge it to full (green light off) then running it until it quits. I'm currently in the second cycle.

author: Connecteur
author_rank: Frequent Contributor
timestamp: January 03, 2022, 02:57:59 am
content: I ran it out for another time. It got to 50 minutes play this time, definitely an improvement. I'll keep deep-cycling as long as I see improvement.

author: geggi1
author_rank: Frequent Contributor
timestamp: January 03, 2022, 04:06:48 am
content: Normally you will get a certain level of improvement by cycling the batteries.I did an experiemnt on some Motorola GP900 NiCd batteries in a battery conditioner charger.At the start the batteries where at 30% and when I stopped the test the batteries where about 85%.That was after about 50c cycles.The charger i used had 5 cycles for each conditioning run. I started one cycle in the morning and one when i left work.I did this for one week.

author: Connecteur
author_rank: Frequent Contributor
timestamp: January 03, 2022, 05:22:44 am
content: Quote from: geggi1 on January 03, 2022, 04:06:48 amI wish I had a conditioner, but all I can do is run the unit until it shuts down, then plug in the adapter to charge it again.

author: not1xor1
author_rank: Frequent Contributor
timestamp: January 03, 2022, 08:02:13 am
content: Quote from: geggi1 on January 03, 2022, 04:06:48 amNiCd are affected by the so calledMemory effectand so cycling might allow to recover some capacity. Ni-MH batteries are unlikely to get any benefit from such a treatment.

author: m3vuv
author_rank: Super Contributor
timestamp: January 03, 2022, 09:47:08 am
content: ive always given mine a shot from a car battery powered battery tab spot welder so shove say 300 amp 12 volt pulse thru them to get rid of dendrides,then just charge them normaly,seems to work for me.

author: Connecteur
author_rank: Frequent Contributor
timestamp: January 03, 2022, 04:15:23 pm
content: Quote from: m3vuv on January 03, 2022, 09:47:08 amI've done that with old Li-ion cells that no longer take a charge, but I use a variable power supply. I start with 30V and a 500 mA limit, watching for it to start taking current. Once the current gets going, I bring the voltage back down to 4V and wait for it to top up. I've brought back quite a few dead batteries that way.

author: Connecteur
author_rank: Frequent Contributor
timestamp: January 03, 2022, 06:15:42 pm
content: I just finished my third deep cycle, and I got about 95 minutes out of it before it died. Still a long way to the original 6 hours, but it'll do for now.In summary,first cycle: 10 minutes run time.Second cycle: 50 minutes.Third cycle: 95 minutes.

author: Shock
author_rank: Super Contributor
timestamp: January 03, 2022, 07:34:44 pm
content: Based on that, I would keep cycling it. If those batteries aren't going to short anywhere you can expose individual cells and measure or charge/discharge a single cell if it needs a bit of help.You can also balance them with just a resistor and another cell, a 1.2 AAA NiMH cell should be fine both charging and discharging at 0.5C or otherwise about 100mAH. They would get warm if abused too much.

author: vjekobalas
author_rank: Regular Contributor
timestamp: January 03, 2022, 07:43:03 pm
content: I've had the unfortunate need to try to fix my Toyota NiMH HV battery - I can't say that I'm an expert, but I knowsomething about the subject. Firstly, the Battery University is a good starting place for learning about this.The NiMH battery cells have a nominal voltage of 1.2V/cell (min 1.0V in case of doing discharge - you can read aboutdischarging to 0.8V but I would not recommend extremes - you will not achieve anything). The NiMH batteryhas a rather flat V/charge graph, so you can't really tell much from the voltage except when it is clear thatone or more cells are dead.The only real way to know anything about the state of the battery is to firstly discharge it down to min voltagemeasuring the capacity, afterwards charge it according to spec and discharge it again to see what chargeit will actually take.From experience with the Toyota battery modules, I can say that you will not know anything until youdischarge/charge a couple of cycles - I've had cells whose voltage looked good butdischarge/charge showed their capacity wasn't even 1/4 of the new battery module, so one could chargethem but they effectively didn't accept the charge / just heated. Only measurementwill tell you something.Here:https://batteryuniversity.com/article/bu-408-charging-nickel-metal-hydrideyou will see other relevant info which indicates the difficulties (temperature, danger of overcharge etc.)with this batterychemistry. In order to properly discharge/charge, ideally the temperature should be measured.This is what happens when you don't have temperature and other parameters under control:https://priuschat.com/threads/2003-prius-stuck-between-2-coconut-trees-for-3-months-now-need-some-help.124157/page-3#post-1775303Here you can see how to use zener diodes to ensure you don't get polarity reversal duringdischarge:https://priuschat.com/threads/got-some-young-2012-modules.139638/page-5#post-1994852

author: Connecteur
author_rank: Frequent Contributor
timestamp: January 05, 2022, 04:39:04 am
content: I just finished the fifth* cycle and it went an incredible 7 hours and 40 minutes. This greatly exceeded my expectations. It was playing at a reasonable volume across the room from my phone, to which it was connected wirelessly. I still have a new battery on order, which I probably don't need, but I'll have a spare.