02 October 2014

Inflated tablet = inflated lithium battery!

Having an inflated tablet with a suspect inflated lithium battery inside the house is not a situation that should last long. Failing Li-xx batteries can release gas or catch fire, something I do not want to explain to my family and neighbours.

So I opened the Mediacom 930i tablet, that was half-open anyway, and finally saw the battery pack inside these devices. My tablet has two 4000 mAh cells in parallel and as expected one of them was puffy:

One of these Li-po cells is 3 mm thick or so: they could make an interesting battery pack for radio use, i.e. to fit inside existing equipment (FT817 and others). The cell on the right, incidentally where the liquid blob and backlight anomalies were, was swollen.

To the touch it felt like a partially inflated baloon.

I measured the voltage across red-black terminals and it read 3.65V: the two cells are in parallel.

What I did next was to carefully remove the blue tape in order to separate the puffy cell, cut its terminals to get it loose and lay it outside in an area where a casual flame would not set something on fire. Interestingly the swollen cell still held the charge. Inside the "battery pack" there was some sort of circuitry that I have not investigated, probably to select the most charged cell.

I was left with one good cell inside a working tablet device. It has been recharged overnight and now we have a tablet 80 grams lighter :-)