I have a Dell Venue tablet which has a removable battery. It’s a good thing the battery is removable, because I’ve now how to replace it once a year over the last two years.
Each battery is made of two LiPO cells. Over time the battery cells begin to puff up. Since there’s no room for the expanding cells, the battery begins to push on the back of the LCD, causing discolored blotches on the screen. Removing the battery makes this issue go away, but why are the batteries dying so fast?
This battery was disassembled, and the monitoring PCB was examined. I didn’t find anything unusual there. The on-board circuit more than likely only protects the battery from being discharged too much, and from overheating (given the thermistor attached).
The voltage on each cell was probed and measured 4.3V. A LiPo cell is fully charged at 4.2V, showing that the cells are being overcharged. Overcharging a cell will stress it and can cause the cell to puff up like mine have.
Unfortunately the problem is with the tablet and not necessarily with the batteries or protection circuit, and that means battery 3 will eventually meet the same fate. I don’t have a solution for this yet except for attempting to contact Dell. Since it’s out of warranty they probably won’t care, but it’s unfortunate they’ve released a product that prematurely destroys batteries.