Hope this photo uploads properly - my first attempt. Assuming it did, this is what my 8 cell NiMH looks like after charging it today. Think it got enough juice? So, what happened? I charged this battery pack two months ago and it's been sitting in storage, unused, since. Same charger (Prophet Sport, 4 - 8 cell NiCd & NiMH charger, 1 or 2 amp setting), same setting ( 1 amp), correct polarity. Blew up about two hrs into the charge. The charger has an auto shift to "maintain charge" after full charge. I hope it was the battery and not the charger, but I'm afraid to put another battery on it. Any ideas? Can I test the charger or does it have to go back to the factory?

A couple of questions to help us figure it out if you don't mind.

what is the batteries capacity?
were all cells hot or just 1-2 or none ?

battery was a known working before this?
charger was a known working before this?

I can conclude only one thing from the info given : the charger delivered about 2000 mah.

To high a charge rate for a Ni-MH pack that has been in storage. Fast charge generates Hydrogen due to overvoltage, pressure builds up, positive tab breaks lose providing iginition source- BANG!

The pack is (was) 1800 mAh NiMH, 8 cell. From the looks of the damage, only one cell blew. I don't know if other cells were hot but the entire plastic overwrap melted down all around. The charger is a small one and was set to 1 amp output and claims to have an overcharge protection circuit. The battery was used last in August but I did put a charge into it a couple months ago and have not discharged it since (other than some minor radio and motor testing - 30 sec max of motor run time). If batteries are in storage for more than a couple months should they be discharged before recharging? The charger instructions pretty clearly state that the charger monitors battery charge and will not overcharge. BTW, the battery is only one year old and was used only a dozen times.

With additional info I would guess that most of the cells had self-discharged a lot, but maybe not the one that blew. Anyways it seems that they were very out of balance to me and the one cell got full long before 2 hrs was up.

Wow that looks dangerous.

So far have only seen Lipo explosion but not NIMH or NICd. I guess you've got to be very careful with whatever batteries we are using as they are all potential risk.

Yeah - very dangerous! Lucky I didn't have a fire. You should have seen my shop. There was fine black dust everywhere and it was a real mess to clean up. From now on all batteries will be charged outside in a steel bucket - or better yet, buy a nitro engine and deal with the slime. I have lost faith in batteries.

Just thought you would like to know - I tried the battery charger on another battery - outside in a metal bucket. It worked just fine. Battery came up to full charge and the charger switched modes to "maintain" and signaled the tone that indicates the charge complete. I now believe the exploded NiMH battery was defective to start with. I will still continue to charge my batteries outside or in the garage (away from flamables) and in a metal container. Am I overly cautious? Perhaps, but having had this happen makes one think twice about things.