5S 21V 30A BMS Battery Protection Board for Power Tools

5S 21V BMS Battery Protection Circuit Board for Power Tools

Keep your lithium-ion battery packs running safely and efficiently with this high-performance 5S 21V Battery Management System (BMS) Protection Board. Designed specifically for 5-series Li-ion battery packs used in electric power tools, this compact circuit board delivers comprehensive charge and discharge protection, extending the life of your battery cells and keeping your tools performing at their best.

Featuring a dedicated 5S lithium battery IC processor, the board continuously monitors real-time voltage, charge/discharge current, and ambient temperature across each individual cell — giving you multi-layer protection in a single compact unit. Made in Mainland China.

Key Features

• 5S Li-Ion Compatible: Engineered for 5-cell series lithium-ion battery packs (18V/21V systems)
• Overcharge Protection: Prevents cells from exceeding safe voltage limits (4.25V per cell) with a 1-second protection delay
• Over-Discharge Protection: Automatically cuts off discharge before cells drop to damaging low-voltage levels
• Short-Circuit Protection: Instantly detects and responds to short-circuit events to safeguard your batteries and tools
• High Continuous Discharge Current: Rated at 40A/50A continuous, with a peak capacity of up to 100A — ideal for demanding power tool applications
• NTC Temperature Sensing: Built-in NTC thermistor monitors ambient temperature to prevent thermal damage
• Ultra-Low Power Consumption: Working current ~25µA; quiescent current ~6µA — minimal drain on your battery pack
• 5S 21V Indicator Included: Visual charge status indication for easy monitoring
• Wide Operating Temperature Range: -40°C to +85°C (RH <75%)
• Compact Design: Measures just 9 × 6.2 × 1.6 cm for easy fitment in most power tool battery housings

Technical Specifications

Why Proper Battery Protection Matters

Selecting and correctly installing the right BMS protection board is crucial to maximising battery longevity and operational safety. This board's multi-protection design ensures your Li-ion cells are shielded from the most common causes of premature battery failure — overcharging, deep discharge, and short circuits.

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Important Notes

• Product photos may not reflect exact size — please refer to listed dimensions.
• Minor measurement differences may occur due to manual measurement.
• Actual colour may vary slightly from images due to monitor display differences.
• Battery and charger are NOT included.

Learn more: OSHA on personal protective equipment

Frequently Asked Questions

Q: What battery configuration is this BMS protection board designed for?

A: This BMS protection board is designed for 5-series (5S) lithium-ion battery packs with a nominal voltage of 18V and a maximum charge voltage of 21V. It is commonly used in electric power tool battery replacements and rebuilds.

Q: What protections does this 5S BMS circuit board provide?

A: The board provides overcharge protection (triggers at 4.25V per cell), over-discharge protection, and short-circuit protection. It also features NTC temperature monitoring to protect against thermal extremes, ensuring safe and reliable operation in power tool applications.

Q: What is the maximum discharge current this protection board can handle?

A: The board supports a continuous discharge current of 40A to 50A and can handle peak surge currents of up to 100A, making it suitable for high-demand power tools that require bursts of high current during operation.

Q: Is the battery or charger included with this protection board?

A: No — this listing is for the BMS protection board only. The battery cells and charger are not included and must be sourced separately.