Some things never change. Both Android phones I’ve owned (Samsung Galaxy S 1 & 2) have this weird bug where the phone turns itself off and when reset by removing the battery the charge level has gone way down.
I woke early this morning to discover the PIN unlock screen so I guessed the phone had rebooted. When I checked the battery levels I saw this. The battery suddenly lost a huge chunk of charge sometime during the night but over the next few hours seemed to recharge itself.
I’d say it’s magic.