Chosen Solution
Maybe six months ago I bought a third-party AC adapter. (Oops.) Since then, the battery usually stops charging at 89%. This last few days, the machine has spontaneously powered down three times. Last night, the battery was at 87% charge; this morning, it was at 0% despite (presumably) hibernating all night. Battery has 101 cycles and is down to 64% capacity. Tried resetting the SMC (shift-control-option/power) without effect. So: Replace the battery. Get an Apple power brick. (Maybe swap out the cable?) Reset the SMC the hard way? What about that voltage regulator? And are there other problems that need to be checked? Thanks. Dan, many thanks for your response. Here is what CoconutBattery has to say:
