I have a mid-2010 MBP with 8 GBs RAM and everything up to date. I use it primarily as a desk top with external display, so it us usually plugged into power supply. Tonight, while trying to solve display problem,(see other post) I worked off battery for a while. When computer hit about 17% power left, I cut itself off. The percentage left was showing the same on two different sources. Anyone know why it quit early? Thanks.