This high-current 4S 40A Lithium Battery Protection Board (BMS REV 2.3) manages and protects four series-connected 3.7V lithium cells (such as 18650, 21700, or 26650 packs). Specially optimized for high-power electric drills and motors, it features an integrated active cell-balancing circuit with 430-ohm precision resistors to maximize cell lifespan and safeguards your projects against overcharge, over-discharge, and high-current overloads up to 40A.