Lithium ion batteries make cordless power tools a lot more practical than Ni Cd. More power for the size, hold charge better, etc.. Mine are Ryobi and the saws were not of much use with Ni Cds. Very useful with Lithium ion. Drills work with either technology but lithium ion will work longer and the drill is lighter.
My batteries tend not to sit still for a week. Not sure how long they would still have a charge. My better two have little 4 position gauges.