My power has tripped quite a few times recently due to some faulty electrical equipment and me doing some testing. One of the issues with this is that the laptop hosting this site has a dead battery so does not stay on or shutdown nicely with a power outage. A new battery is $35, so I thought I would give repairing this one a shot.
I pulled out all my old laptop batteries and tested the cells for capacity. The old cells were rated for about 4.6Ah and tested at
1st pair 2193mAh
2nd pair untested/dead
3rd pair 1714mAh
So after a couple of days testing I found 3 pairs that tested at
1st pair 3726mAh
2nd pair 3701mAh
3rd pair 3858mAh
I soldered them into place and topped them up individually to 4.2v to balance them. As a side note, the balance circuit was humming when I had attached the batteries initially, I assume it was trying to balance them.
Plugging it into the laptop gave a fast flashing light of the charge LED saying there was an error. The laptop reported something wrong with the battery, and being charged to 0%. I unplugged the mains and the laptop stayed on-yay. I plugged the mains back in and had the same error- boo. So at this point the laptop would use the battery until it was flat then not charge it again. I just made a single use battery :-).
So, I left it charging for about a month and it got up to 12%. I figured that if I discharged it it would re-calibrate and I would be left with a fully calibrated battery. This was not the case. It lasted a few hours and when I powered it back up it no longer even recognizes the battery is connected. Grr.