I believe German Metabo/Hitachi is or has released a new line of power tools with a combination battery and corded in one tool. There is some information beginning at 20:00 of this video:
https://www.youtube.com/watch?v=BRQYafS77Rc Why it has taken manufactures this long to release a combination like this I don't know? I use very few power tools these days, so kind of out of the loop, do other manufactures have this option now?