I went out to the truck this morning and go to start it..... nothing. DOH! :dohh: I left the lights on and drained my new (2 months old) battery dead as a door nail. After giving myself a BIG dope-slap :no: I was able to jump it from my car and drove it the 15 miles to work. After getting to work, I tried shutting the truck off for a minute and then starting it up again. It did start up, but the volt gauge stays right on 13 where it used to be higher. Hopefully it's just the alternator trying to charge up the battery. Have I ruined my battery by draining it all the way down? :dum:

Running it down once won't hurt it. I don't think 15 minutes was enough for the battery to charge all the way back up, which is why the voltage was reading a little lower than normal. Just keep driving it and the voltage should go back to normal.

Thanks for the feedback Dave, it helps take the worry out of it.
Guess I'm going to have to add a headlight buzzer/reminder!

It usually takes more than that to kill em for good. It should be fine.

Thanks for the feedback guys! I drove it up and back to my friend's place last night to give it a good charge-up, about an hour and a half round trip on the highway. Now the volt meter is showing higher. Not completely back up to where it used to be, but much better now.

Running it down once won't hurt it.

Running it down completely once won't kill it, it most definately does hurt it. Running a starting battery below about 90% charge is damaging to it. Running it completely dead is pretty bad even for a deep cycle battery. It won't kill it, but it definately has taken a hit in capacity and life expectancy.

An alternator is designed to maintain charge not "charge up" a discharged battery. Anytime you accidentally discharge a battery, your best bet is to take it out and put in on a charger. Your alternator has to work harder to try and charge a discharged battery and in eventually will overheat and need to be replaced or rebuilt. A conventional Battery is only designed to be discharged and recharged (called a cycle) a small amount of times before it needs to be replaced. One time isn't going to do too much damage, but the fewer times you leave your lights on, the longer the battery and charging system will last.