In the morning, the phone was still hot - I thought, no big deal, it's just been charging.
Then the battery charge started rapidly disappearing again. Cold reboot helped.
Trivial analysis would offer an educated guess - there was a runaway process consuming CPU and power. Too bad BlackBerry in production configuration doesn't offer any diagnostic tools...
So I just wrote it off as a weird bug.
Until the next time it happened, few days later.
Primary suspect: Google Maps for Mobile. Not everything is clear at this point, but it seems that the necessary conditions are:
- fetching driving directions;
- following the route;
- driving through a no reception zone (not sure).
Interestingly enough, a similar problem was reported for iPhone 3G (read this, search for "draws") - apparently, it is possible to drain the battery faster than the power adapter charges it.
Last time, it was possible to stop the drain by closing Google Maps - it took me a few tries, however, and I'm not sure how exactly did I get the BlackBerry out of that condition. Let's see if this happens again, and what would Google do to Maps to fix this.