alex- in the future, plug a battery tender while you're fiddling with your stereo for setting up eq's and stuff.
it's only like $20 on amazon and works very well. whenever i want to play something on my car stereo while in the garage with engine turned off, i just plug it in. heck, my Z is always plugged in during the week since i only pull her out on the weekends.
if you have a heavy setup you might want to get a digital battery charger and use 2A while you fiddle with your eq's and amps, etc.