NiMH batteries strange charging behavior - Page 1
Forum section: electronics / beginners

author: Ichisuke
author_rank: Contributor
timestamp: February 13, 2023, 05:45:57 pm
content: Hi everyone. Hope I can find an answer here. I'm no expert at all in electronics things so hope I can write everything correctly.So I have some Energizer rechargeable batteries, 4 are rated 2000mAh, 2 2300mAh.I have this Sony charger, model BCG-34HRE, with a refresh function. At the time I read that this was one of the best charger... don't know if it's true or not.It charges the batteries individually, on the back it says 1050mA(AA)x2 525mA(AA)x4 I don't know why they put the output values in couple since you can charge the battery one by one.Anyway I have this issue, basically the 2 2300mAh batteries won't charge inside the charger, no matter how much charge there is in the batteries I just get a red blinking light.Also they won't charge in another charger, a Duracell one but that can only charge 2 or 4 batteries at once.Then I have a Logitech mouse that can also recharge one battery inside via usb cable, it charges at 180mA.If I put the energizer batteries in the mouse I can charge them just fine, also if I put the batteries when they are still warm from the mouse in the Sony charger they start charging normally. When the charge is finished if I remove them from the charger and then put them back in, the charger won't recognize/charge the batteries again...What's wrong with these batteries? The charger was charging them fine time ago. Why do they charge only at "slow charge" inside the mouse?

author: Zero999
author_rank: Super Contributor
timestamp: February 13, 2023, 09:00:14 pm
content: The batteries are probably bad, or failing. A smart charger will look at the voltage and impedance and decide not to charge them, because doing so could cause them to heat up and catch fire. Your USB mouse has a dumb charger, which will charge them regardless, but at a very low current. It's definitely safe to use charge them at a low current, but don't expect them to last very long.

author: Ichisuke
author_rank: Contributor
timestamp: February 13, 2023, 09:19:34 pm
content: Okay thanks. I think I'll just trash those 2. I'll buy new one when the others will stop working too.

author: temperance
author_rank: Super Contributor
timestamp: February 13, 2023, 10:09:00 pm
content: NiMh batteries don't like sow charging. They become high resistance somehow.They can be revived by charging them from a power supply with appropriate current limiting, say one amp to too 3V. At first the voltage will rise up to something above 2...2.5V without any current flowing trough the batteries. Then all of a sudden they become alive, current increases and the voltage drops to a normal level.An other way to revive those is to apply a short circuit. (seen on this forum somewhere) But I can't recommend that as it might cause fire.I've seen this on low cost and expensive NiMh batteries.

author: wasedadoc
author_rank: Super Contributor
timestamp: February 13, 2023, 10:35:26 pm
content: Quote from: temperance on February 13, 2023, 10:09:00 pmCodswallop.

author: Zero999
author_rank: Super Contributor
timestamp: February 13, 2023, 10:59:51 pm
content: Quote from: wasedadoc on February 13, 2023, 10:35:26 pmSlow charging is fine. I think he was referring to trickle charging i.e. continuously leaving the battery connected to a low current, which will eventually damage it, unless the current is really low, say under1/50C.

author: temperance
author_rank: Super Contributor
timestamp: February 14, 2023, 02:05:17 am
content: @ wasedadoc24 years ago I made NiMh battery charger to charge 36 packs, 4.5V, 2Ah at once. There was plenty of time to charge the batteries so the design was a set of resistors, switches and a timer for each channel. (charge current just under C/10)After a while the customer started complaining about failing batteries. We setup a test and recorded data for about 100 packs daily. Load around 350mA with under voltage cutoff. Balance between cells ok. And indeed slowly but steadily the batteries would stop to accept any charge. In the end, the battery voltage would go above 2V/cell and no current would flow when charging. Fast charging those failing batteries with a 0.5...1C current from a 5V source would bring them back to life and they would perform for an other two...three months on a slow charger.I have no idea why those batteries became high impedance after a while. (tested with two different well known brands. Both suppliers stated there is nothing wrong with how we charge those batteries...)Nothing fancy to develop. But things quickly became a disaster with 1000 chargers out there, 3600 battery packs and no good answers after 6 months non stop testing.

author: MrAl
author_rank: Super Contributor
timestamp: February 14, 2023, 11:50:30 am
content: Quote from: Ichisuke on February 13, 2023, 05:45:57 pmHi,A smart charger will test the batteries for quality and possibly decide not to charge them.A really good charger will test the batteries for internal resistance and throttle down the current to the battery cells. They will still charge but only at the rate that the charger deems to be low enough to not overheat the cells.So although the cells may charge slower on some chargers it doesnt mean you cant use them, just that they will never perform the way new batteries or semi new batteries will perform. In some devices this doesnt matter because they only use low current anyway. In other devices they will appear to lose charge quickly or not work at all.

author: Ichisuke
author_rank: Contributor
timestamp: February 14, 2023, 11:56:34 am
content: Quote from: MrAl on February 14, 2023, 11:50:30 amThanks. And do you have a model of a very good charger to suggest? Since I'm actually in need of other batteries too I'd gladly buy a better charger.

author: BILLPOD
author_rank: Frequent Contributor
timestamp: February 14, 2023, 02:46:15 pm
content: Good Morning Ichisuke, I have one of these and I LOVE it. I connect itto my computer with a USB cable and program the charging, or discharging any way I want; all parameters are adjustable. It's not cheap, but it will do all you want. Look here:https://www.amazon.com/SKYRC-MC3000-SkyRC-Multi-Chemistry-Charger/dp/B075HRVJ4Q

author: Ichisuke
author_rank: Contributor
timestamp: February 14, 2023, 04:13:47 pm
content: Oh well that's a bit expensive for some casual charging... But thanks anyway!

author: MrAl
author_rank: Super Contributor
timestamp: February 14, 2023, 08:11:37 pm
content: Quote from: Ichisuke on February 14, 2023, 11:56:34 amHi,Yes i use the Opus BT-C3400 and have been using it for some years now.It will charge Li-ion 18650 cells, and the smaller 14500 cells, and AA, and AAA NiMH and i think NiCd too.It might do more than that but i only have used it for the 18650 and 14500 Li-ion cells and AA NiMH cells.It displays voltage, charge current, time, and ampere hours charge.It also has a discharge function so you can test your rechargeable cell to find out if it is still up to it's ampere hour rating.Charge current up to 2 amps but that's only for 2 cells, if you charge 4 cells i think it's down to 1.5 amps each or maybe 1 amp each.It also has a 12v cigar lighter cord so you can charge in the car but i dont think every one comes with that or it may increase the price.Not sure if you like the prices, but they range from $50 to $60 now on Amazon. I got mine some time ago when they were only around $40.

author: Ichisuke
author_rank: Contributor
timestamp: February 14, 2023, 09:33:43 pm
content: Quote from: MrAl on February 14, 2023, 08:11:37 pmMmm it seems pretty much impossible to find here in Italy.

author: MrAl
author_rank: Super Contributor
timestamp: February 15, 2023, 10:45:30 am
content: Quote from: Ichisuke on February 14, 2023, 09:33:43 pmOh not even Amazon?

author: Ichisuke
author_rank: Contributor
timestamp: February 15, 2023, 11:23:05 am
content: Nope. But I know that the Panasonic charger with the display should be a very good charger too.

author: MrAl
author_rank: Super Contributor
timestamp: February 15, 2023, 11:53:38 pm
content: Quote from: Ichisuke on February 15, 2023, 11:23:05 amWow that's amazing i thought Amazon shipped almost everywhere.

author: IanB
author_rank: Super Contributor
timestamp: February 16, 2023, 01:56:30 am
content: Quote from: Ichisuke on February 13, 2023, 05:45:57 pmI just noticed that you wrote "Energizer" batteries. There was a time, a while back, that Energizer rechargeable batteries were really bad quality and almost doomed to fail and stop working after a while. It's possible your failing batteries might be some of that kind.As for charging, I do own and sometimes use a fancy charger with a display and control buttons, but most of the time I just use a "set it and forget it" charger. The Panasonic BQ-CC17 works well for me, especially with Eneloops or Panasonic cells. It's not especially fast, but it has four individual charging circuits and smart charge termination on each slot. It's fine if you can wait overnight for charging.

author: MrAl
author_rank: Super Contributor
timestamp: February 16, 2023, 12:01:07 pm
content: Quote from: IanB on February 16, 2023, 01:56:30 amHi,You just reminded me about my experience with the "Energizer" cells too in the distant past.I purchased four of the AA size standard NiMH rechargeables and found they had such a bad self discharge that they would almost completely drain in two days. I wrote to the company and they sent me a coupon for four more. I went to Walmart and got four AAA size instead to try them, and same thing. I stopped buying Energizer anything and went to Eneloops.I also had an Energizer fast charger for AA and AAA. It worked for a while then quit completely. No more anything from them.I wrote to the company about that and explained the way they could easily put a charge control on the fast charger so people could choose to charge their cells slower for longer life. They sent me back a letter that said they could not accept any new ideas because they might have already thought of that and it may be in the works already.All i can say is that has to be one really dumb company and i wont have anything to do with them again.Eneloops seem to be the go-to AA or AAA rechargeable cells now. There are other types of low self discharge i have tried too and with good results. There was a brand "Kodac" low self discharge NiMH and they worked good too.One set of Eneloops and they will last for a long time. I have some several years old that still work good.

author: Ichisuke
author_rank: Contributor
timestamp: February 16, 2023, 03:55:34 pm
content: Thanks everyone. I'll probably grab that Panasonic model that IanB wrote since it comes with 4 batteries already and costs 30€.Yeah these are not the first energizer batteries that I throw away because they simply stop charging.