"Is there a battery out there that will basically power a stereo and fans without draining to fast?"
I think it was a Looney Tunes cartoon
doing a sendup of the dutch boy trying to plug
the dike. If you try to solve this one piece at a time, you're going to wind
up playing Twister, on the holes in the dike.
Get one of the inexpensive books
on 12v electrics (or spend hours longer chasing aorunf on the web) because you need to size and match the charging
system, the battery(s), and the loads in order to avoid unpleasant expenses or surprises.
A battery that lasts longer? Sure, some types but mainly "How big can you afford to buy or carry?" except that also means you need to put more energy back into it, which means the charging
system upgrade. Catch-22, if you don't plan for the entire system, you'll wind
up redoing it more than once, or cursing each time the battery dies.