The 4-volt lithium-ion battery provides a number of features such a long run time and long-shelf life so your batteries will always be ready for action. The 4-volt lithium-ion battery powers the Ryobi Tek4 family of professional electronic tools and Ryobi 4V power tools — there's a ton of them (motion-sensing alarm shown here) and we've tried them all out. Trust us, they're pretty sweet. For FREE information, visit http://pb.hotims.com/23726-353