4S 40A BMS Lithium Battery Protection Board with Cell Balancing
This 4S 16.8V 40A Battery Management System (BMS) is a compact protection board designed for 4-cell series lithium-ion battery packs built with 18650, 26650, or polymer lithium cells. It combines overcharge protection, over-discharge protection, over-current protection, short circuit protection, and active cell balancing in a single, easy-to-wire PCB.
The board handles a continuous discharge current of up to 40A, making it a practical choice for power-hungry applications such as electric drills, cordless motors, sprayers, and LED lighting systems. Charging is supported at up to 20A maximum continuous current, with an input charging voltage of DC 17V–18V.
The integrated cell equalization function automatically balances the voltage across all four cells during charging, reducing wear and improving the usable lifespan of the battery pack. Wiring follows a straightforward 0V, 4.2V, 8.4V, 12.6V, and 16.8V scheme via solder pads, keeping the installation clean and reliable.
At just 45 × 60 × 4mm, the board is compact enough to fit inside most custom battery enclosures while delivering the protection features required for safe, long-term operation of high-capacity lithium packs.
Package Contents
1 × 4S 16.8V 40A Li-ion Battery Protection Board (BMS)
