21V 5S Li-ion BMS Protection Board for 18650 Battery Pack DIY

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.