Almost any loudness at 2 hours will drain your battery, not a problem. You can do this, but youd need to jump start and ud be fine.
Im surprised that yours lasted 2 hours, i learned quickly never to park in an empty lot during a rainstorm with your girlfriend listening to music. I think my batt died in 45min - 1 hr (guess).
Nothing was more embarrassing then "Hey stephen (my brother), you think you can come jump start me?"
"Yea sure, where are you at?"
"This empty lot... , with Mary."
"Haha, im commin, same shit happened to me before"