# Rechargeable batteries for flash get really really hot



## DeepSpring (Jun 15, 2007)

I have the energizer rechargeable 2500mah batteries and the little charger that slides into itself for storage. When I charge the batteries in it they get really really hot and I just wanted to check if this was normal. Is it ok to put them in my flash so hot or maybe stick em in the fridge for a few minutes first?


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## Mike_E (Jun 15, 2007)

In something like this I don't know if I'd trust just anybody to keep my flash from melting/bursting into flame.  Have you been to the battery maker's web site and looked through their FAQs?

mike


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## sabbath999 (Jun 15, 2007)

Cold will kill part of your charge in that type of battery. If you are concerned, just let them cool down... also, if you are using the charger provided by the manufacturer and matching batteries, you will be OK. Don't know why it would be THAT time sensitive that you couldn't wait a couple minutes between taking them out of the charger (yes, it is normal for them to get warm) to putting them in the flash.


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## mysteryscribe (Jun 15, 2007)

I expect mine to get hot but it scares holy hell out of the wife when she touches them while plugged in.


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## DRodgers (Jun 15, 2007)

I've tossed 15min chargeable energizers into my sb800 hot numerous times and have had no problems.

I would however recommend that you let them cool naturally first though just to be safe.


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## Big Mike (Jun 18, 2007)

That's the problem with small chargers...I think I have the same one...they don't dissipate the heat very well.  Excessive heat is what may eventually shorten the life of your batteries.  

This is why it's better to have a bigger charger...some of them even have cooling fans I think.  Personally, I charge mine in my office where already have a fan.  I just put the charger in front of the fan and it keeps the batteries cool.

Actually, I'm thinking of getting a better charger anyway.  I don't like that my small charger doesn't tell me how much of a charge they have.  It just has a light to say they are charging.  My camera batter charger at least flashes to tell me how much is left to charge.


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## newrmdmike (Jun 18, 2007)

i had a duracell explode (kind of, not quite as dramatic as it sounds) in my sb-800

ii could hear stuff bubbling out of it, and opened the compartment up, the batteries were rediculously hot, and one had acid coming out of the end, like boiling out.

i don't use rechargables . . . but i like the energizer e^2 aa's, they are just really expensive.


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## NJMAN (Jun 18, 2007)

I have this exact same one as well, and just noticed yesterday again after charging them that they got very hot.  I let them sit at room temperature for 15-30 minutes before I put them back into my 580EX speedlite, that is, if I have enough time to do so and not rushing off somewhere to use my equipment.  But sometimes I dont have a choice.  It doesnt seem to affect the proper functionality of the speedlite.


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## shingfan (Jun 18, 2007)

batteries getting hot is an indication of over-charge.....some charger are stupid and they keep charging your batteries even though they are full.....the excess electrons have no room to fit but turn into heat and dissipated.


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## shorty6049 (Jun 18, 2007)

i have that happen all the time with my energizers. i have a 15 minute quick charger  and they get hot when i use that, havnet used a regular charger in a while though...


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## DeepSpring (Jun 18, 2007)

Thanks for the info. Usually there is ample time to let em sit first but there are those times when you just have to run off to a shoot.


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## flyingseale (Jun 24, 2007)

NiMH cells charge with an exothermic chemical reaction, so they will get WARM when charging.  Also, most chargers simply charge for a set time which means the cells are not only warm from the proper charge but they get HOT due to overcharging.  If they get too hot the pressure builds up and they 'vent' which you'll notice as a hissing noise.  Bubbling is fine...hissing = vented.  In extreme cases, you'll not only get gases escaping from the vent, but the electrolyte too.  This is potassium hydroxide in NiMH, which is a very strong alkali...so wash your hands properly and be careful not to get it in your eyes.
Whilst this might sound scary there is no need to worry about using them hot.  In fact they perform a lot better when they are warm.
If you are concerned about how hot they get the only solution is to get a decent charger that monitors the charge of each cell individually and terminates it when complete.  Here's a couple of examples from Maplin in the UK.
http://www.maplin.co.uk/Module.aspx?ModuleNo=217900&criteria=battery charger&doy=24m6

http://www.maplin.co.uk/Module.aspx?ModuleNo=105064&criteria=battery charger&doy=24m6

BTW, if your charger is several years old it might only be designed for NiCd cells.  Charging NiMH on a NiCd charger will also make them hotter than expected due to the different charge algorithm.

Mike


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