Battery temps when charging - Should I be worried?

New here, be gentle.

I have a bunch of Eneloops (Sanyo & Pana), IKEA Ladda, Powerex batteries.

My first charger was a Maha Powerex C9000. It serves well but I wanted more slots. I bought a Maha Powerex MH-C800S 8 slot charger. I noticed that the charge speed was too high and go annoyed setting Soft charge each time. I also noticed that the batteries got really hot, even on soft charge. Thinking it was due to the tight spacing spacing of the slots, I decided to get a Nitecore i8 which has a large gap between batteries, away from electronics, 1c charge speed default. The batteries also get hot.

I recently read that the C9000 detects voltage rather than -dv. I don't really understand the technical, but I'm clued on enough to 'get it'. The C9000 results in only slight warmed batteries.

I don't have a heat measuring so HOT to me is: Holding cup of tea, when ready to drink. 40C-45C...I think...

So the question:
Does hot batteries at charge affect longevity? Should I be worried?

In retrospect I should have just forked out for another C9000.

Which cells are getting hot? The problem with the 8 cell Maha charger is you cant really set the charging rate on it. Think the high is 2000mAh and the low is like 900mAh. I dont know for sure though. The C9000 doesnt fully charge the cells and tops off at the end since Nimh cells get warm or hot at the end of the charging cycle. I only use the Eneloop chargers or the C9000 to charge Eneloops or other high end NiMH cells.

Actually you are doing ok with two nice chargers - but know this:

Eneloops are low-impedance cells that can actually handle 1C charging (2000mah typical), even though they may get uncomfortably warm near the 1 hour mark.

Nimh in general are exothermic, meaning it is *normal* for them to get warm/hot.

But what IS hot, and what is damaging hot?

Hot is when you can pull a cell from the Maha charger, and put it into your palm (not just the end of your pinky finger) without immediately dropping them to the floor blistering hot. You may have to roll them in the palm a little but that's ok. Blisters aren't.

With *Eneloops*, the difference between charging for approximately an hour until uncomfortably hot, and a slower .5C (half the rating) for 2 hours instead all touchy-feely has about the same affect. It's all about how well a cell is manufactured, and the current vs time. So the default of 2000mah is ok - you didn't need to use the slow-charge all the time.

The time you may want to consider switching to the slow-charge method with Eneloops is when they are nearing the end of their life, and internal resistance is rising. Typically just before the charger kicks them out when it does it's test. You can tell this by applying the "palm holding/rolling" method. Blistering hot now - drop to the floor - use the slower charge.

Things change when you use normal nimh batts, or other lsd types that aren't so keen on low internal resistance. Use the slower charge method if you can't hand-hold them.

For me, with Eneloops it's not just a matter of being able to charge them faster - they ARE the best in the industry, even after years of non use. Try that with a Powerex batt after a few years, and the charger may just kick them out.

I guess what I'm trying to say is that the average consumer doesn't know it's OK for nimh to get uncomfortably warm - provided the cells are truly high-quality, and the charger is also. Even Maha succumbed to the pressure to put out a lower-current version, because hey, the customer knows best, not the battery manufacturer.

I charge up my NiMH at 1A and don't have any heat problems with my Maha C9000/Opus BT-3400.

My LaCrosse BC-700 trips the thermal protection as a rule, at 700mA. Hot, hot, hot.

I have spoken, so it shall be.

Chris