I own the first 'remolded' revision of the Macbook released in '08 (5,1), and have had it for over a year now. Recently though, after 10 or so minutes running off just battery power (fully charged), it shuts down unexpectedly. It doesn't say the battery is low, or near low, it just shuts down. It's really annoying, I have to use the charger wherever I go. I really need my laptop so I don't really want to take it to an Apple Store and have to wait a week to get it fixed, unless it's really necessary. My software is up to date. Any ideas on what my problem is/how to fix it?