A Battery Management System, or BMS for short, is used to protect your battery during charging and discharging. This 3s BMS is fairly easy to install, but will require that you are decent with a soldering iron to add the charge/discharge/balance wires (and you can get the wires here or the connectors here). Suitable range: For nominal voltage 3. 6v 3. 7v lithium battery(including 18650, 26650, lithium polymer batteries)product size: 55mm x 41mm x 1. 4mm material: Metalcharging voltage: 12. 6v maximum output current: 40a maximum output power/charging power: 252w.