FLAGPOWER 18V 4.0Ah Liion Cordless Tools Replacement Battery for Milwaukee XC 48-11-1815 48-11-1820 Brand New | Li-ion | 18 Volts | 4000 mAh | Black 100% Compatible with MILWAUKEE 48-11-1815 48-11-1820 48-11-1840 M18 Batteries are made with the highest quality materials Integrated microchip prevents overcharging & lengthens battery life Exercise the Battery - Do not leave the battery dormant for long periods of time. We recommend using the battery at least once every two to three weeks. If you don't plan on using the Power Tool Battery for a month or more, store it in a clean, dry, cool place away from heat and metal objects. Ni-Cd, Ni-MH and Li-ion batteries will self-discharge during storage; Remember to recharge the batteries before use.