The 4S 14.8V / 16.8V 20A Li-ion Battery Protection Board is a high-performance BMS (Battery Management System) designed to protect 4-cell (4S) lithium-ion battery packs — specifically those using 18650 cells — from overcharge, over-discharge, and overcurrent conditions. With a 20A continuous discharge rating and balance function, this board is engineered for moderate to high-drain applications including power banks, e-bikes, RC vehicles, portable power stations, and energy storage systems.
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:
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Overcharge protection — Disconnects the charger when any cell voltage reaches approximately 4.25V to 4.3V, preventing damage from excessive charging.
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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.
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Overcurrent protection — Disconnects the output when current exceeds 20A, protecting against short circuits and excessive loads.
The 4S configuration means the board manages four cells in series, balancing the voltage across all four 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 20A continuous rating makes this board suitable for moderate to high-drain applications such as power banks, e-bikes, RC vehicles, portable speakers, LED lighting, and portable power stations. This is a step up from standard 4S boards that typically max out at 5A–10A, providing additional headroom for more demanding projects.
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 (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 DIY power banks, e-bikes, portable speakers, and RC vehicles.
Important Note: This BMS is designed for 4S (4-cell) 14.8V/16.8V lithium battery packs using 18650 cells, with a maximum continuous current of 20A. For higher-current applications, a BMS with a higher current rating should be used. 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 4S 18650 battery pack for a power bank, assembling an e-bike battery, or adding safety protection to an energy storage system, the 4S 14.8V / 16.8V 20A Li-ion Battery Protection Board provides a reliable, high-current solution. It is suitable for individual makers, students, and businesses purchasing in bulk for product development or educational programs.
Features
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4S quad-cell protection — Manages four 18650 cells in series with cell balancing
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20A continuous discharge — Moderate to high-current capability for demanding applications
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Balance function — Ensures even charge and discharge across all four cells
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Comprehensive protection — Overcharge, over-discharge, and overcurrent protection
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18650 compatibility — Designed for the most popular lithium-ion cell format
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Solder pad design — Supports both direct soldering and spot welding
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Compact PCB design — Sized for space-constrained battery packs
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Wide application range — Power banks, e-bikes, RC vehicles, portable power stations
Technical Specifications
| # | Parameter | Specification |
|---|---|---|
| 1 | Compatible Battery | 4S 14.8V lithium-ion (18650 cells) |
| 2 | Full Charge Voltage | 16.8V |
| 3 | Continuous Discharge Current | 20A |
| 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 4S packs |
