18V, 1.5AH Lithium-ion Battery, Built In Memory Chip, Memorizes The Usage History & Communicates With The Charger, Less Weight, Lithium-ion Battery Weighs 40% Less Than Ni-MH Or Nickel Cadmium, Anytime Charge, Lithium-ion Batteries Have No Memory Effect & Can Be Charged At Any Time, Charging Technology Controls Current, Voltage & Temperature To Maximize Battery Life.