My wife inadvertantly left the dome light on on our '03 Echo in the summer when the car was only a year old. The car wouldn't start the next morning...completely dead. Her father had a brand new battery, never used, and that new battery would no longer hold a charge. I learned a lesson then not to let a battery go dead even if it's new as it was useless after a couple of years sitting idle. Most know about that probably, but this warning is for those that don't.
I had that happened not too long ago. The trunk didn't close properly and the trunk light drained it. The moment I found it didn't start, I pulled it and sat a computer power supply on top of the -ve terminal, +12V to the +ve post, turned it on and ran it overnight. It won't properly charge this way, so the next day I took it to crappy tire for a test. Turns out to be still good and they charged it for free. As of this moment it still holds a charge.
Try my computer power supply trick. It may save a car battery or two down the road.
(EDIT: I'm in a pinch and don't have a proper charger. If you have one, by all means use it.)