Batteries "very" hot after a charge/discharge/charge cycle

[Loa]

Hello,

I have 8 NiMH AAs (2500Mah Energizers) that I bought about 2 years ago. Since getting 16 Eneloops, these first batteries don't get used much.

When I got my Maha C800s charger, I decided to put those older batteries through 2-3 deep Charge ->- Discharge -> Charge cycles to "revive them".

They work alright, but I'm concerned about how they become "very" hot at the end of the charge cycle. Hot enough that I cannot leave my fingertips on them for more than a few seconds.

Is that normal? And is using a small fan to cool them during charging a good idea?

Thanks a lot,

Loa

 

[Mr Happy]

No, it's not normal, but it is also not unusual. When charging NiMH batteries it is normal for them to get "very warm" but if they get "very hot" that is not the best. It is to be hoped that your eneloops do not get that hot?

When batteries get very hot during charging it is a sign that they are in poor condition. If they do not improve after a few cycles there is nothing much you can do about it except to recycle them and replace them with new and better ones.

 

[Lynx_Arc]

It depends on the rate of charge as to how hot they should get. If you charge at 1amp and up rates batteries will get rather hot. Using a fan to cool them is fine the energizer 15 minute charger has a fan built in to keep batteries cooler as it can really cook them fast.

 

[Loa]

It depends on the rate of charge as to how hot they should get. If you charge at 1amp and up rates batteries will get rather hot.

Sadly I'm not sure just how fast my charger recharges in its cycling mode. It's a Powerex Maha C800s. I know it can charge at 1 amp (fast) or .5 amps (soft) charge modes, but I'm pretty sure it charges even slower than that when using the cycling mode. (And that's when my energizers got hot...)

I also haven't checked my new eneloops at the end of a charging cycle... I'll do that next time.

Thanks for the info,

Loa

 

[TakeTheActive]

...I have 8 NiMH AAs (2500Mah Energizers) that I bought about 2 years ago. Since getting 16 Eneloops, these first batteries don't get used much.

When I got my Maha C800s charger, I decided to put those older batteries through 2-3 deep Charge ->- Discharge -> Charge cycles to "revive them".

They work alright, but I'm concerned about how they become "very" hot at the end of the charge cycle. Hot enough that I cannot leave my fingertips on them for more than a few seconds.

Is that normal? And is using a small fan to cool them during charging a good idea?

New and/or healthy cells usually do not get hot at charge rates of 0.5 - 1.0C.

That said, older cells charging at 0.5C on my 'old' LaCrosse BC-900 get hotter there (tight spacing) than when I'm charging them on my 'new' Maha MH-C9000 (wider spacing). And, on either charger, the outer two cells are always cooler than the inner two cells.

So, you're 'Neglected' (2500Mah Energizers) "that I bought about 2 years ago" are not healthy. I would suggest running a few 'simulated' Maha MH-C9000 / Industry Standard Break-In Cycles (Charge @ 0.1C for 16 hours; Discharge @ 0.2C; Charge @ 0.1C for 16 hours; Use in a device; Repeat as necessary.)

Using a fan on some 'Smart' Chargers defeats the OVER TEMPERATURE protection. Personally, if you can't condition / cycle them at a lower / cooler charge rate, I'd have to consider them ready for the "Recycle Bin".

On the other hand, if you're willing to invest the effort, you COULD monitor them during the 'Too High a Current' Charge Rate and manually remove them from the charger when they reach ~120°F. They're 'unhealthy'. That's why they're getting HOT. If you can try 'nursing' them back with a lower current, they might respond more favorably. HEAT = DAMAGE.

BTW, although I've never owned any, Energizer 2500mAh cells have a BAD REP here on CPF - SEARCH the Archives. :thumbsdow :sigh:

 

[CanadianGuy]

I'm also trying to figure out if my panasonic AA nimh's are bad. Using the charger that came with them (Panasonic BQ390) they don't stop charging. It used to be that the charger would blink green until about an hour later when it would stay solid green.

Now it just keeps on blinking. I think this is a smart charger. Months ago, it started clicking loudly every minute, but hasn't lately. I didn't know what was making the sound, so I went looking and realized it was the charger. Must be over-charge protection. I don't think the charger is bad, I think it's the batts. They are from 2003 and haven't been used in any high draw apps (when I was a kid, I used to love using my RC car, and I assume that those cause batts to have a shorter service life)

Oh, and I couldn't find a thread about charging other brands of nimh batts with my panasonic bq390. In my job, I am recovering old remotes and some people forget their rechargeables in them!

 

[Black Rose]

So, you're 'Neglected' (2500Mah Energizers) "that I bought about 2 years ago" are not healthy. I would suggest running a few 'simulated' Maha MH-C9000 / Industry Standard Break-In Cycles (Charge @ 0.1C for 16 hours; Discharge @ 0.2C; Charge @ 0.1C for 16 hours; Use in a device; Repeat as necessary.)

The Maha C800S does not allow you to set the charge rates. It's either 1000 mA or 500 mA

The spacing on the C800S is pretty tight, similar to the BC-900 I think, so there isn't much room for air circulation around the cells.

 

[clintb]

Ah, how quickly people forget the past.

Energizer + AA + 2500 = lots of problems reported.

Try running some cycles for fun, but I'd be willing to bet they're toast. Do yourself a favor and email Energizer to, possibly, score some vouchers. And for your good batteries, just get some Eneloops.

edit: Scratch getting the Eneloops; you already did! I was focussed on the bad, bad Energizers.