Last night I left my MacBook Pro running on battery power and went to bed. This morning I could not boot the thing. I kept hitting the power button and nothing happened. After having been plugged into its power supply for several minutes, it finally booted. I guess there is no way for this thing to use AC power directly. The battery needs some charge before it can start. This is not true of my old R40 Thinkpad or my G4 iBook.
That was scary. I was sure I had a dead Mac.