Exploding torch

I use NiMH batteries for lots of things. I always ignored the warnings about Hydrogen gas given off.

On my last trip one time in the middle of the day I reloaded my uw light which takes 8xAA. I can't remember now whether the batteries had only just been charged or whether they had been sitting around for a long time. In the back of my mind is an idea that they might have been hot after recharging at the time when I loaded them.

I sealed the light, and left the room. A few minutes later there was a load BANG (even though I wasn't in the room my hearing was affected for the next 10 minutes or so) and I went back in to find that the body of the torch had split and the whole thing was too hot to touch. Fortunately no fire ... All the batteries were just sitting in their brackets, looking exactly as usual (except that normally I wouldn't be ale to see them as they were inside the light).

It looked as though it was just caused by gas pressure rather than any combustion... only after a few days I suddenly realised I should have taken a pic. After all, there were 2 cameras right there! Most of my friends would be much mroe interested in that, rather than in all the u/w critter shots.

I spent the rest of the trip worrying about whether the other equipment was safe. And I started opening things with the lids facing away from me in case a sudden release of pressure might blow the lid off and into my face when I opened things.

So here's my question: Under what circumstances does gas build up? Does it depend on whether the batteries have just been charged? On temperature? On the current drawn from the battery? Or what? What procedures reduce the risk of an accident? Should I switch to another battery type?

-David

Yes, there is a good chance of gas venting from rechargables... This is why all Sea & Sea battery caps are fitted with a gas valve - My YS120 suffered it in Dec 99. Scared the crap out of everyone on the boat.

Ideally, batteries should rest for an hour after charging is completed.

That is how I ran my recharges in Roatan. They come off the rapid charger rather hot so I generally made sure they were charged well in advance. I was like work sometimes. Back form the dive, change and charge batteries, download...Seemed to work

You don't want to put them on charge while they are hot either. Some NiMH chargers have temperature sensors but most do not. If the battery is too hot the charge cutoff circuitry may not work properly. Most of the risk comes from overheating either through improper charging, too heavy a load, or too deep a discharge...and of course continuing to operate them while hot.

Many AA chargers seem to produce hot batteries. This really shouldn't be the case. Ideally the cells should go in cool, stay cool while charging, and get slightly warm when charging completes. If your batteries come out consistently hot, you may want to consider another charger or different batteries.

I'll check into that as I am using the Kodaks, and charger. Had no problems with the charger shutting off when complete though.