This is interesting. My battery was at 94% or so, and then shut down for no discernible reason. When I turned it back on, the battery displayed 1%. I charged it up to about 5% and then it jumped to 50%. Then upon restarting again, it dropped to 2%.
Edit: I should point out that I'm running a CyanogenMod 10.2 nightly, and I'll probably crosspost this there once I've done some more research.