as a newbie i don't yet know the "dos and don'ts", so forgive my ignorance, but what about vehicle remote cells?
12V 23A 1/2 AAA alkaline batteries. Small/lightweight with a fair longevity. i've never used them for anything with motors, so i don't really know their limitations, but couldn't these be rigged to fit the purpose or are the 12V 23A just too much? Price isn't excessive either.