Similar to the Fire-Breathing Dragon. It's when the girl is giving you a blowjob, and you thrust her head down all the way down making her think you're about to climax, but instead you magiacally pee in her mouth and it comes squirting out her nose just like a dragon.
Pay no attention to that other definition. The REAL battery acid is a mixture of a sparks energy/alcohol drink with 2-4 shots of your favorite vodka, preferrably a citrus, making one hip drink. The term "battery" comes from the striking similarity the can has to an energizer battery. Just hook it up and get ready to party.
Partygoer #1: Check out Teo on the dance floor. How's he able to blow up so huge?!
Partygoer #2: Must've had some battery acid.