Type of Battery: Lithium-ion. Voltage: 20V. This battery pack contains 10 pieces 3.7V 18650-4000mAh Lithium-ion batteries. Only weighs 1.6 lbs. Compatible with WORKPRO 20V: Well compatible with WORKPRO New Series 20V Cordless Power Tools such as drill, impact driver, impact wrench, angle grinder, reciprocating saw, grass trimmer and hedge trimmer. (For W122046AE/W004581AE/W122035A/W004572A/W125042A/W125051A/W125050A/W159006A/W159008A and more) Power Indicator: 4 indicator lights on the Battery Pack for recognizing battery charge status immediately. Much Safer: Safeguard features against incorrect voltage, battery overload, short circuits, and internal overheating. No memory effect, can be charged freely. Environmental-friendly: Innocuous to the environment. All 5 pieces lithium-ion batteries in the battery pack accord with the certification requirements of CE/GS/EMC/PAHS/ROHS. WORKPRO 20V 4.0Ah Lithium-ion Battery Pack