I have a "mature" T650 that has recently developed a problem with the battery.
Sometimes, with the charger plugged in, the battery status drops quickly.
It can go from 40% down to 15% in a few minutes. Then, if I disconnect from the charger, the battery status will go back up to near the original amount, say 37%.

It's not clear what's causing this. I'm running, Chatter, VeriChat, and have BT enabled, though it is not connected when this happens. I've disabled the always-on feature of VeriChat and I've turned off Chatter, and it doesn't seem to make a difference. I've also bought a new battery and the behavior is the same. I've run BatteryGraph, and it reports the drops and rises just as with the battery indicator.

Has anybody seen this behavior? Software bug? Hardware problem?