HOT NiCd with no charge.

[ifoxbox]

Hi,

I repair Sonicare toothbrush handles which use NiCd batteries in them. I received an Elite handle that did not work out of the box. I was told that the handle was never used and that it was untouched out of the box. They said that it had been in the closet for a couple of years, and had never been used. Anyway, when I opened the handle to remove the battery, I noticed that the positive end of the battery was black, and the back of the PC board was burnt up. I was just curious, what would make a battery that was just sitting heat up like that?



Here is a picture of the back of the PC board. You can see where the positive end of the battery went, and where it burnt up the surrounding area.

 

[SilverFox]

Hello Ifoxbox,

Perhaps the cell shorted out...

Tom

 

[Brlux]

I once had a generic green wraper MiMH AA cell internaly short out for no reason. It was in a mini mag flashlight that I was werring on my belt and if I recal the cell was an 1800mah and fairly new probably within the first 5 charge cycles. I noticed the smell of something hot and felt a warm sensation on my hip through Jeans and the holser. When I puled the light out it was to hot to hold. I set it aside and waited for it to cool down. there was no blackenin of anything but I think the heat shrink was split.

 

[speederino]

I had an alkaline short out internally recently. Picked up the TV remote and noticed it was warm. Figured the cat had been laying on it or something so I proceeded to watch some TV. Noticed a little while later it was still warm. Popped the battery cover and sure enough, one of the AA's was warm. A few hours later it was cold and totally dead. I can't imagine a cell with low internal resistance like a Nicd or nimh doing it....hot potato!

 

[ifoxbox]

Hello Ifoxbox,

Perhaps the cell shorted out...

Tom

Hi Tom,

I think that is probably it, but what do you think would make a NiCd that has supposedly not been used short? This is not the first time I have seen this happen in the new Elite handles. I figure that the battery in the handle had probably been sitting on the store shelf for a few years not being used, and then stored in a closet for a while. Just sitting should not cause a cell to short right?

Thanks!

 

[SilverFox]

Hello Ifoxbox,

Cadmium migration has been linked to this, but it usually occurs during extended trickle charging. Self discharge tend to form larger crystals, and it may be that a bump caused damage to the separator.

I have not run across this, so I am just guessing...

Tom

 

[ifoxbox]

Thanks for letting me know.