The 5S 18.5V / 21V 18650 Lithium Battery Protection Board (BMS) is a high-performance safety module designed to protect 5-cell (5S) lithium-ion battery packs — specifically those using 18650 cells — from overcharge, over-discharge, and overcurrent conditions. With a balance function and robust protection circuitry, this BMS is engineered for a wide range of applications including power tools, solar energy storage, and LED lighting systems where reliable battery safety is essential.
At the heart of the board is a BMS protection circuit that continuously monitors the voltage of each cell and the total pack current, disconnecting the load or charger if any parameter exceeds safe limits. This protects both the battery pack and your connected devices from damage, extending battery lifespan and ensuring safe operation.
The board provides three critical protection functions:
-
Overcharge protection — Disconnects the charger when any cell voltage reaches approximately 4.25V to 4.3V, preventing damage from excessive charging.
-
Over-discharge protection — Disconnects the load when any cell voltage drops to approximately 2.5V to 3.0V, preventing deep discharge that can permanently damage the battery.
-
Overcurrent protection — Disconnects the output when current exceeds safe limits, protecting against short circuits and excessive loads.
The 5S configuration means the board manages five cells in series, balancing the voltage across all five cells to ensure they charge and discharge evenly. This cell balancing function is critical for maintaining pack health and maximizing lifespan. Without proper balancing, one cell can become overcharged or over-discharged, leading to premature failure or safety hazards.
The 5S configuration provides a nominal voltage of 18.5V and a full charge voltage of 21V, making it suitable for a wide range of applications that require higher voltage than 4S packs. This voltage range is ideal for power tools, solar storage systems, and high-power LED lighting.
The board features a solder pad design that supports both direct soldering and spot welding. The exposed pads allow you to solder wires directly to the board, while also being compatible with spot-welded nickel strips for professional battery pack assembly. The board includes B+, B-, BM1, BM2, BM3, BM4 (mid-points), P+, and P- pads for battery and output connections.
The 18650 compatibility makes this board ideal for building custom battery packs using the most popular lithium-ion cell format. 18650 cells are widely available, reliable, and offer excellent energy density, making them the preferred choice for power tools, solar storage, and DIY projects.
The wide application range includes:
-
Power tools — High-current protection for drills, saws, and other tools
-
Solar energy storage — Protect 5S battery packs in solar storage systems
-
LED lighting — Reliable power for high-power LED lighting systems
-
Portable power stations — High-current protection for portable power
-
E-bikes — High-power protection for electric bicycles
-
Electric scooters — Safe power for personal mobility devices
Important Note: This BMS is designed for 5S (5-cell) 18.5V/21V lithium battery packs using 18650 cells. Always verify the voltage and current ratings match your application before installation. Ensure all wiring and connections are rated for the maximum current your application will draw.
Whether you are building a custom 5S 18650 battery pack for a power tool, assembling a solar storage system, or adding safety protection to an LED lighting project, the 5S 18.5V / 21V 18650 Lithium Battery Protection Board provides a reliable solution. It is suitable for individual makers, students, and businesses purchasing in bulk for product development or educational programs.
Features
-
5S five-cell protection — Manages five 18650 cells in series with cell balancing
-
Balance function — Ensures even charge and discharge across all five cells
-
Comprehensive protection — Overcharge, over-discharge, and overcurrent protection
-
18650 compatibility — Designed for the most popular lithium-ion cell format
-
Wide voltage range — 18.5V nominal / 21V full charge
-
Solder pad design — Supports both direct soldering and spot welding
-
Compact PCB design — Sized for space-constrained battery packs
-
Wide application range — Power tools, solar, LED lighting, e-bikes, portable power
Technical Specifications
| # | Parameter | Specification |
|---|---|---|
| 1 | Compatible Battery | 5S 18.5V lithium-ion (18650 cells) |
| 2 | Full Charge Voltage | 21V |
| 3 | Continuous Discharge Current | Variant dependent |
| 4 | Overcharge Protection Voltage | ~4.25V – 4.3V per cell |
| 5 | Over-discharge Protection Voltage | ~2.5V – 3.0V per cell |
| 6 | Balance Function | Yes |
| 7 | Connection Type | Solder pads (spot welding supported) |
| 8 | Module Dimensions | Compact PCB for 5S packs |
