My current (2007?) MacBook Pro laptop battery dies in the arse at 78% if I leave it disconnected. I always leave it connected so I guess that goes to show. My

My current (2007?) MacBook Pro laptop battery dies in the arse at 78% if I leave it disconnected. I always leave it connected so I guess that goes to show. My previous iBook G4 battery also had some problems, but it died closer to 20%.