It definitely depends on what type of work you predominantly do, if it is mainly demo than I can see a lot of batteries because there isn't much measure twice cut once time on stuff like that but if you do more fastening then maybe only two or three as you can do a ton of screws with a 4ah battery now a days. The other thing that matters is do you have other "accessories" like a radio, heated hoodie, that type stuff that isn't really a tool but yet takes up a battery or two.