[Azimov]

That would have to be tested, but it could be a problem. Not that it would discharge the battery, but it may cause a short. But I'm not sure. A rubber cover to seal them would work. A lot of testing and customization would need to be done to make it work right.
I've seen RC subs that just left the motors exposed to the water and they worked fine. The voltages in these things is very small and complete water proofing may not be needed, Though I would anyways.
The stock charging tabs could be replaced with a jack that's plugged when not in use. Probably better anyways since you don't wanna flop a wet truck on the charger or have to dry thoroughly every time either. I'm sure it could be done, but it would require some work.
The main problem is corrosion. When I was building Aquabots (small, solar powered aquatic robots) I found that no matter how you waterproof a container to hold your electronics and motors, the air pocket created rises and falls in humidity as the external temperatures change. This places a light mist on the electronics that corrodes them over time. I've tried pulling a vacuum, dessicant, and all sorts of voodoo to stop this. The best solutions seem to be encasing in epoxy or wax. Or, filling all voids with thin mineral oil so no air remains.
Like I said, it would take some serious customizing and testing to pull it off, but it is doable.