First of all, no - there's no rule that says your battery had to be concealed when it's on the robot.
If, for some reason, you are thinking about putting the battery on the outside of the robot ... I'd think again. Like Andy A. said, one hard hit and it could get cracked or fall off. Placing the battery inside the robot chassis does take up a lot of space, but it protects the battery a heck of a lot better (assuming it's strapped down and all - not just thrown in there.)
This is what 93 has been doing for as long as I've been associated with the team. Check this out:
That's the bare-bones of TOBOR V (2002.) The battery sits, on it's side, on a piece of polycarb, swiss-cheesed for weight. Two small pieces of polycarb are glued on the first piece, so they sit on either side of the battery, when it's in. There is *just* enough room for the battery to fit in between these pieces ... it's a pretty snug fit. To keep everything in place, a single buckle-strap goes from "top to bottom" and is tightened, once the buckle is ... buckled. Of course, once the battery is connected, the connection is zip-tied for security.
It's simple, easy to make, pretty light-weight, and your battery won't fall out!
