Specifications : B1 the connect point between battery 1 and battery 2 B2 connect the point between battery2 and battery 3 B3 Connect the point between battery 3 and battery 4 B- connect to battery negative end P- + connection charge / discharge positive; P- connection charge / discharge negative Note : 1) this board is not suit high power electronic tools, if use for screwdriver and drill, please don’t buy. 2)Above 3A device,means the battry discharge rate is more than 3C. 1C rated battery, 2000mah equals 2ah*1=2A max working current. 3C rated battery means 2ahx3=6A Max working current. 4S LI-ION BMS Specifications : Over Charge Voltage:4.25-4.35v±0.05v Over Discharge Voltage: 2.3-3.0v±0.05v Max working current:10A Max Peak current:20A Working Temperature:-40~+50 Storage Temperature:-40~+80 Small current: 6uA Life cycle:50000hours Resistance:45m? Short cut Protection:Protectable ,change for repair Size: 3.6×3.5cm/1.42×1.38 inch Quantity: 1 Piece Note : The lithium battery protection board is not included the welding tabs.