BMS 4S 20A Protection Board 18650 Li-ion Lithium Battery is an electronic regulator that monitors and controls the charging and discharging of rechargeable batteries. Battery BMS protection boards are the brains behind battery packs. BMS 4S 20A Protection Board 18650 Li-ion Lithium Battery manages the output, charging, and discharging and also provides critical safeguards to protect the batteries from damage. 18650 protection circuit Board is a high-accuracy voltage detection circuit. The 20A protection board can be used for lithium-ion Phosphate batteries, Low power inverters, massager battery packs, electronics, LED light backup power supplies, solar street lights battery packs, and many other products