I am sorry for omitting the fact that I attached a cigarette adapter then plugged in a usb adapter that outputs 5v. It doesn't keep up with the drain. The battery is a 12v 7amp hr.
I use my Nexus 7 with an aviation app. I have a dry cell 12v battery that I plug the Nexus into but the main battery still drains. Any ideas on why or other ways to add an aux battery?