[KenWittlief]

keeping the air tank topped off until the last minute before a match makes sense, because your pneumatics might be leaking a little bit. Putting a shutoff valve right after the tank is the best way to keep the tank full till the last minute.

but your battery should not be 'leaking charge' while its on your robot, esp unplugged. Having a big RV battery in your cart could be somewhat dangerous: they are full of acid, and if it got shorted by accident then Yikes!