Can't speak for the Milwaukee but I have a bunch of 20v Dewalt batteries and they last for at least several months between uses. They can sit all winter in the shop and still work for long periods in the spring without another charge. Milwaukee should be just as good. The DeWalt impact driver I have has been up to every challenge I've handed it. It's nice not being tethered to a hose. I have a pneumatic impact tool (probably Chinese) and never use it. It'll last forever I guess.