18 V (5.0 Ah) Li-Ion Battery. 5.0 Ah battery offers maximum run time for prolonged, heavy-duty applications. LED charge level indicator displays approximate remaining battery power. Battery protection system provides over-discharge, temperature and current protection for enhanced performance, battery cycle life and overall battery life (when used with STAR marked tool). Li-Ion Batteries offer extended run time versus Ni-Cad and Ni-MH batteries. Li-Ion Batteries offer more cycles over the life of the battery versus Ni-Cad and Ni-MH batteries. Optimum charging system utilizes 3 Active Controls (Current, Voltage and Temperature) to maximize battery life. Built-In memory chip communicates with Charger CPU to optimize the charging process based on the unique conditions of each battery.