21V 5S Li-ion BMS Charging Protection Board for 18650 Lithium Battery Packs

Build safer, longer-lasting DIY battery packs with this compact 21V 5-Series (5S) Battery Management System (BMS) / PCM Protection Board. Designed for 18650 lithium-ion and lithium polymer (LiPo) cell configurations, this module monitors and safeguards your battery pack automatically — giving you confidence in every build.

Key Protection Features

Overcharge Protection – Prevents cells from being charged beyond safe voltage thresholds, extending overall pack lifespan.
Over-Discharge Protection – Cuts off output before cells drop to damaging low-voltage levels.
Short Circuit Protection – Instantly interrupts current flow in the event of a short, protecting your cells and connected devices.
Balanced Cell Management – Supports 5 series-connected lithium cells for a nominal 21V output, ideal for power tools, e-bikes, and DIY electronics.

Specifications

Configuration: 5S (5 cells in series)
Compatible Voltage: 21V Li-ion / LiPo battery packs
Compatible Cells: 18650 lithium-ion and lithium alloy batteries
Package Contents: 1 × BMS/PCM Protection Board
Size: As shown in product images
Country of Origin: Made in China

Who Is This For?

This BMS board is perfect for electronics hobbyists, makers, and engineers building custom battery packs for power tools, RC vehicles, e-scooters, portable power stations, and other 21V DIY projects. Whether you're assembling from scratch or replacing a faulty protection circuit, this module is a reliable, cost-effective solution.

Important Notes

Due to manual measurement, please allow a tolerance of 1–3mm.
Product color may vary slightly from images due to monitor differences — please refer to the actual item received.

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For general guidance on lithium battery safety standards, visit the U.S. Consumer Product Safety Commission – Lithium Battery Safety.

Learn more: Battery management system

Frequently Asked Questions

Q: What does a BMS (Battery Management System) protection board do for a 5S lithium battery pack?

A: A BMS protection board monitors and manages your battery pack's voltage, current, and temperature. For a 5S 21V lithium pack, it actively prevents overcharging, over-discharging, and short circuits — all of which can permanently damage cells or create hazards. It is an essential component for any safe DIY lithium battery build.

Q: Is this BMS board compatible with 18650 lithium-ion cells?

A: Yes. This 5S PCM/BMS board is specifically designed for use with 18650 lithium-ion cells as well as lithium alloy (LiPo) cells arranged in a 5-series configuration, producing a nominal 21V output — commonly used in power tools and DIY electronics projects.

Q: How many cells does this 5S BMS board support?

A: This board supports 5 lithium cells connected in series (5S), resulting in a fully charged voltage of approximately 21V. It does not support parallel configurations on its own — additional hardware would be required for series-parallel (e.g., 5S2P) arrangements.

Made with care

Great value

Elegant design

Quality materials

This product is crafted with quality materials to ensure durability and performance. Designed with your convenience in mind, it seamlessly fits into your everyday life.

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