Batteries are the weakness for cordless power tools.
My DeWalt set was great on the job being used daily. But when I went to work for a company that supplied cordless tools, my set got taken home for occasional homeowner use.
The batteries slowly lose thier ability to hold a full charge. I replaced them after the use life dropped off to just a couple of minutes, but the newer ones suffer the same problem of lack of use causing a slowly diminishing use life on a full charge time on the charger.