> There are some adapters to allow mixing batteries, for example this one allows using Black & Decker 20V batteries on Bosch 18V tools
DeWalt, Craftsman, Porter Cable, Black and Decker, and probably another brand or two that I can't recall at the moment all use very close to the same batteries. The pins are in a different order and there's small plastic tabs in certain places so you can't swap brands but with a little bit of work you can charge a Craftsman battery in a Porter Cable charger and use it to power a DeWalt drill. Don't attempt to modify these batteries and chargers unless you have an understanding about what you're doing, though.
DeWalt, Craftsman, Porter Cable, Black and Decker, and probably another brand or two that I can't recall at the moment all use very close to the same batteries. The pins are in a different order and there's small plastic tabs in certain places so you can't swap brands but with a little bit of work you can charge a Craftsman battery in a Porter Cable charger and use it to power a DeWalt drill. Don't attempt to modify these batteries and chargers unless you have an understanding about what you're doing, though.