BMS 4S 18650 Lithium Battery Protection Board (40A-14.8V) is an electronic protection circuit board (BMS — Battery Management System) designed for 4 lithium-ion batteries connected in series, commonly using 18650 cells.
Battery Type:Li-ion / 18650
Battery Configuration:4S
Nominal Voltage:14.8V
Full Charge Voltage:16.8V
Max Discharge Current:40A
Max Charging Current:20A
Balancing Function:Yes (on some models)
Protection Functions"Overcharge, short circuit, overcurrent
Operating Temperature:-40°C to +85°C
Pin Function
B-:Battery negative
B1:Cell 1 connection
B2:Cell 2 connection
B3:Cell 3 connection
B+:Battery positive
P+:Output positive
P-:Output negative
Important Note
This board is mainly a protection board (BMS).
You still need a proper 16.8V lithium-ion charger for charging the battery pack safely. Reddit electronics communities frequently point this out because many sellers call it a “charger board,” which can be misleading.
Common Applications
DIY power banks
Solar battery packs
Cordless drill batteries
Electric scooters
UPS systems
Portable electronics