I last drove it Sunday; how could the battery be dead by Thursday?
Well, for one thing, it's a bit shy of eight years old.
For another? When I pulled it out two weeks ago I noticed that one of the caps was loose, as in "nearly off" loose, thus venting half the cells to the environment. I thought that my own efforts at removing the battery had dislodged it, but it's possible it was loose before that--and if so, who knows what kind of crap got into those cells?
For a third, when a battery is not grounded right and the alternator isn't producing quite enough voltage to charge it correctly, that can have deleterious effects on its longevity. Lead-acid batteries are very tolerant things, and can take a lot of abuse, but when you get to this end of their lifespan that abuse catches up with you.
I've had it on the trickle charger overnight, and it ought to be full of electrons now. I suppose the thing to do is to take it off the charger and see how long it lasts, but what I really need to do--soon--is to get a new battery in it. That'll only be about a hundred bucks. *whimper*
Or, you know, take her for a spin every day to make sure she's charged up. Who knows how long the battery has been like this, only I've been driving 450 miles a week so it was always fully charged?