If you are mainly thinking of certifications, then an internet forum really is not the right place to get help. Regarding liability you need information that is liable for you - and that´s nothing you can get here.
Anyhow, I think this is a very constructive forum here, so let´s keep it that way: I know the US is not like Europe, but usually you find ways to bring a useful product to the people. Why don't you sell the housing design on a 3D-print-platform together with the BOM for the batteries and the charger? I´m no lawyer, I don't think this removes ALL responsibility from you but I assume it takes it to a reasonable level.
Of course, you can't earn big money that way. But there´s nothing like a free lunch...