What happened to my battery pack?

So I used to use 2 4AA battery packs for my lights. I've since replaced one of those packs with 18650s, but I still use one of them. I've used my new Kodak NiMH batteries on a few rides without problem. Today I noticed that one of my lights stopped working after a couple of minutes. I finished the ride in, took apart my battery holder, and look what I found:





The 18650 pack was not touching the AA pack at all and the light still works with a different pack.

It appears to have been a short, but there is nothing in the holder that could have caused a short. Could it have been bad batteries? These aren't more than 3 weeks old and have only been used maybe 4 or 5 times due to battery rotation. Ideas? I'm glad it was my "safe" NiMH and not my lithium ion.

It looks like that cell vented. Did you ever drop or overcharge the cell? That can cause lowered capacity. Then, if you put it in series with good cells, reverse charging and can occur once that cell is fully discharged.

lolzertank said:

It looks like that cell vented. Did you ever drop or overcharge the cell? That can cause lowered capacity. Then, if you put it in series with good cells, reverse charging and can occur once that cell is fully discharged.

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All the cells were at the same charge level, but they were charged in the new Kodak cheap charger that came with them. They measured 5.6 volts together coming off the charger, which is normal for my AA packs. I'll probably toss the charger anyway, too slow, even for a slow charger.

What is this pack powering? I have a similar looking 3 cell holder that succumbed to high current.

this looks most like a short "first" meaning even if your cells puked it looks like the inital problem was a bad short. or to high of current for the pack, and no cooling.

I spy a VERY CHEAP nasty 9V battery snap! If you are going to use these packs please use the nice rigid plastic ones. The cheap ones tend to begin to wear and a few braids of the copper snap. I bet this is what happened - making it heat up a lot when any significant current is drawn.

Way too much Amp draw for those holders. IIRC, they're only good for 1A max. The first picture tells the story; springs got hot and melted through! Yikes.

sylathnie said:

What is this pack powering? I have a similar looking 3 cell holder that succumbed to high current.

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It powers a R2 P60 dropin.

clintb said:

Way too much Amp draw for those holders. IIRC, they're only good for 1A max. The first picture tells the story; springs got hot and melted through! Yikes.

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Good to know. Luckily I have new 18650 holders, so I won't need the AAs anymore. I'm glad it was my backup light, you know how the hills are from Vilonia to NLR, especially in the dark.