[FrankJ]

The safety aspect can be dealt with fairly easily. Cost and complexity still remain. The battery powered tool industry has pretty much gone to Li ion for everything except the bottom line tools. They get badly abused and have a low risk of fire/explosions. First could pick one or two commercial solutions and restrict maximum current draw and require specific chargers.

Another option for Arduino and PIs is somebody to package it with a battery and case. As long a it a company and they make it available for sale, it becomes a legal COTs device. (insert the usual future rules disclaimer here). Make it nice enough and maybe AndyMark would stock it for you.