The Dual batteries connected in parallel for additional c apacity and range, and the switcher can manage the two batteries on your bike. It will detect the voltage of the two batteries in real time. When one battery is exhausted during riding, it will automatically switch from one battery to the other, again for you Powered by the electric bicycle, or support two batteries to simultaneously supply power to your electric bicycle intelligently and balancedly. Note: 1. Do not confuse the positive and negative connectors on the dual battery switch. Make sure that the power of both batteries is turned off before connecting. 2. Both batteries must have the same voltage 3. Suitable for maximum 30A or maximum 40A controller ( Optional ) Water resistant Applicable voltage: 20V72V Compact Size and Weight 30A version:6*4.5*1.8 cm 110g 40 A version:7*4.5*1.8 cm 130g