What kind of tanks are you trying to build? Have you thought about a Lift-Off top attached by magnets? That would make it very easy to remove and charge the battery. Or perhaps the system invented by Darryl Turner and now used in the brand new js2 that just came out? That has one small lever underneath the bottom that you flip and then the top lifts up from the front kind of like the hood of a car. Either that or the magnet system would make it very, very easy to open the tank and remove the battery.