29 May 2015

MacBook Pro battery - not a happy end

Once charged, the 3S(eries)2P(arallel) Li-po pack from a MacBook Pro, was not too keen to keep the top voltage. Each cell parallel slowly decreased voltage from 4.20 V to 4.05 V or so in a couple of days at rest.

So I plugged my usual discharge load: a 12 V / 5 W automotive lamp. It drained about 350 mA. Then I left it there unattended for a couple of hours when the pack voltage had reached ~11 V.

When I came back I found a very faint lamp and this:

Six heavily inflated Li-po cells!! No heat. No smell (these square cells have a sweet smell when they loose gas - and it's toxic of course!).

Each parallel was at 2V thereabout. I took the pack outside and vented each cell to prevent explosion from excessive pressure. Not a big loss since it would not retain enough energy. I have always admired the battery duration on Apple laptops and I think they did a good optimization job in their energy management processes, both software and hardware. A depleted Apple battery is probably really exhaused and not good for reuse.

Morale. Do use a discharge protection circuit if you care of Li-xy cells!