One real good way to seal a hole in a metal object, is heating and cooling duct tape. That's the sticky back aluminum foil stuff.
Very good stick compared to most tape. I used to use it regularly to do a temporary repair on a windsurf board, then fix it right when I got back home from vacation. No problem sticking underwater. But if the box got pressurized, the thin aluminum would pop before the box could distort. Nowdays there is good duct tape again, so gorilla tape would work just as good I bet.
The aluminum tape is very paintable too.
Another option would be to simply change the way the lid is held down. Remove the bail, and secure the lid with someting less sturdy. Tape, zip tie, something that would break in time if the lid needed to be forced up.
Same foil tape is ideal for covering holes in motor covers, btw. So you can run sealed, but open up to let water out once a month or so. It's high temp tape for hot ductwork.
THE LIPO RULES. NEVER ABOVE 4.3V NEVER BELOW 2.7V DON'T PUNCTURE
Ideal charging /discharging range for Lipo, 3.65v minimum 4.1v maximum
See battery technology section, FAQ thread at the top of the page for lipo noob info.