Sudden crashes and drops in battery charge Recently I've experienced random and sudden crashes on my Galaxy S2. There is no warning or shutdown message. Suddenly it's just powered off. What could cause this? Is there any way to see what was going on just before the crash? I've also noticed odd drops in battery charge like this.

I'm running the official Android 2.3.5 ROM from Samsung.
You might need to reset the battery stats anyways.  Drain the phone entirely -- when it shuts off, turn it on again until it shuts off again and repeat until it won't turn on.  Then wipe the stats and charge to 100% with the phone off (leave it plugged in for an hour or so after it appears to be fully charged).  Turn it on, drain it again, and charge to 100% while off again without wiping the stats this time.

Of course, if you're not rooted you can't wipe the stats, but the drain/recharge cycles should help regardless by providing fresh stats.