The BLACK+DECKER LBX2040 40-Volt MAX Lithium Ion Battery, 2.0 Ah has been formulated for longer runtime and improved performance. These batteries will a charge for up to 500 days between uses, but will need to be recharged before use after that time. They are 25% lighter then NiCd batteries and 34% smaller, with no Memory Effect. It also features a state of charge indicator to allow you to see how much charge is left. The LBX2040 40-Volt MAX Extended Run Time lithium battery is compatible with the 40-Volt line of outdoor power equipment which includes string trimmer, hedge trimmer, sweeper vac, chain saw and other power equipment. Maximum initial battery voltage (measured without a workload) is 40 volts. Nominal is 36.