A battery impact will likely have more power than a corded model. They have more power than a lot of air impacts. I have a friend who is a professional mechanic. He works on everything from motorcycles to 18 wheelers. He said after he got his Milwaukee 18v cordless impact he hadn't used any of his air impact wrenches in years.
The new Lithium batteries hold a charge for a very long time with no charging in between. I sometimes use 3 or 4 different Milwaukee M18 cordless tools on and off thru a workday. Many days I never charge a battery.
