Drove my 940t earlier today, and it started right up. Left it for an hour, came back, and the battery is completely dead. Barely enough juice to unlock the doors, never mind start.

I never had any warnings of the alternator not doing it's thing, and the starter sounded pretty perky when I cranked it a couple of hours before. The battery is pretty old, and I was just thinking about getting round to replacing it. But I had anticipated some warning of sluggish starting or other adverse signs. Is it common for a battery to fail so quickly, or could it be the sign of bigger trouble, like some kind of short circuit or grounding problem?

Any thoughts or similar experiences greatly appreciated!

It is a lot more common to have a battery cable connector "sudden death".
If it were mine I would test the battery and clean the terminals before
deciding it is dead. Then I would check the charging system.
Normally batteries just sort of fade away. Enough of a load to make it
die instantly would probably also start a fire or at least cause smoke or heat.
--
George Downs, Bartlesville, Oklahoma, Central US

It's pretty common with "no maintenance" batteries; I've had the same thing happen a couple of times, myself,
I'd check for current drain, too.
--
Jim McDonald

Unusual but not impossible: if the battery develops an internal short, it will toast in short order. Most battery failures occur either in very hot weather or at the first frost in the Fall. If it is older than five years, it was on its last legs anyway.

Thanks very much for the input everyone. I realized that in the past few days the battery's had a lot of load:

I started the car a good 12-15 times in a row to flush the transmission on Monday - plus, today was a hot one, and I was forced to sit idling in traffic with the A/C on to preserve some groceries for quite a while. Probably toasted it then.

I'll throw a new one in tomorrow and hope for the best!