Background: our 2005 Acura TL has been a little slow on the draw lately when starting from cold. Probably getting time to replace the battery, but it's been working, so no rush. Then, our daughter spilled some milk in the back seat. Milk that had been in a sealed cup, under the seat, rotting away, which we hadn't noticed. End result: stinky, sour milk all over the carpet.

Okay, off to the car wash to get the whole damn thing shampooed.

Once back in the garage, We left the doors and roof open. I knew this would kill the battery, but our daughter has a habit of turning on the interior car lights and we don't always notice (result: dead battery in the morning). Every other time, the car has jump-started as normal. Not this time.

I hooked the TL up to our Audi A3. I had the Audi running and the TL off for a few minutes. I hop into the TL. The dome lights and everything else come on at full brightness. I turn the key. Click! Then the car was completely dead. No dome lights. No nothing. I let the battery charge for a few more minutes. Nothing. Totally dead car.

Theory #1: the battery was a goner and this killed it.
Theory #2: we blew a fuse.
Theory #3: (seen on the Internet) we blew the main relay.
Theory #4: (also seen on the Internet) the battery terminal connector, somewhat corroded, needs to be replaced.

Any idea what might have really happened and, more importantly, how I'm supposed to diagnose this? I could go borrow a voltmeter to check the battery and fuses. I could go and pre-emptively buy a new battery, drop it in, and see if that helps.

Thoughts?

The first thing I'd do is check the battery terminals. Just disconnect the battery and see if there's a lot of corrosion. Clean them with a wire brush either way. Reconnect. See what happens. It'll probably still need to be jumped.

Could also be a dead cell in the battery. Try jumping the car with the battery removed.

The fact that the lights stopped working make me wonder if you blew a fuse though. Do they still do nothing?

edit: By dead cell I mean shorted.

I borrowed a multimeter at work today. I'll test the fuses when I get home tonight. My guess is that I must have nuked a fuse (or worse) by virtue of the fact that several minutes connected to the good, running car failed to provide an iota of juice to the lights. A shorted out cell in the battery could also yield the same result, I suppose.

One way or another, looks like I'm replacing the battery.

Another handy trick for corroded battery terminals is to pour a can of coke on them. The carbonic acid in the soda dissolves the buildup on the battery terminals. I've started many a car with a can of pop.

All the fuses checked out. The battery registered 2.5V. We took it to the auto parts store. Their battery tester said it was fubar. We bought a new one, put it in, and everything worked perfectly. Problem solved. Yee haw.

P.S. While the car had been sitting, the emergency brake managed to seize up. Luckily, toggling it on and off about ten times fixed it. I love cars, really I do.

Glad it was simple.