4S Lithium-Ion 18650 Battery Balance Board (14.8V / 16.8V Full Charge Balancing Circuit)

The 4S Lithium-Ion Battery Balance Board is a highly specialized add-on circuit designed exclusively to equalize the voltage across four series-connected (4S) Lithium-Ion cells. While many standard, budget-friendly Battery Management Systems (BMS) offer vital over-charge and short-circuit protection, they frequently omit the crucial cell-balancing feature. This standalone module bridges that gap. It is designed to be wired in parallel with your existing standard BMS to upgrade your pack with professional-grade passive cell balancing.

The board operates on a straightforward but highly effective principle: passive resistive bleeding. During the final stages of a charge cycle, it actively monitors each of the four cells. The moment any individual cell reaches the maximum capacity of 4.2V, the board activates a dedicated micro-resistor for that specific tier, bleeding off the excess energy as a tiny amount of heat. This temporarily halts that specific cell from overcharging while allowing your charger to continue pushing current to the remaining lower-voltage cells until the entire pack is perfectly synchronized at 16.8V.

Key Features & Functional Advantages:

• Precision Voltage Equalization: Ensures every cell in your 4S pack reaches exactly 4.2V, capturing 100% of your battery's true capacity and preventing localized cell degradation.

• Universal Companion Module: Designed to be easily retrofitted into existing battery packs. Simply solder its balance leads to the main nodes of your battery alongside your standard, non-balancing protection board.

• Low-Profile Footprint: The incredibly thin, minimalist PCB design allows it to be easily heat-shrinked over a 4-cell 18650 array without adding unnecessary bulk to your project enclosure.

• Heat-Dissipating Design: Utilizes large, high-quality surface-mount resistors to safely and consistently bleed excess voltage as heat during the final trickle-charge phase.

Perfect For:

• BMS Upgrades: The perfect companion board for upgrading a cheap, standard 4S protection BMS that lacks an integrated balancing feature.

• DIY Power Walls & Inverters: An essential addition for maintaining the health of high-capacity 14.8V storage banks built from salvaged or mismatched 18650 laptop cells.

• Custom Robotics Power: Ensures your 12V-class robotic chassis batteries deliver maximum runtime by keeping all cells perfectly matched after heavy discharge cycles.

• Pack Repair & Maintenance: A great bench tool for manually bringing a severely unbalanced 4S drone or RC car battery back into perfect equilibrium.

Technical Specifications:

• Configuration: 4S (4 Cells in Series)

• Supported Chemistry: Lithium-Ion (18650, 21700, LiPo) with 3.7V nominal / 4.2V peak rating

• Balance Trigger Voltage: 4.20V (± 0.03V) per cell

• Balance Recovery Voltage: 4.19V

• Balancing Current: ~66mA (Varies slightly by specific resistor load, typically 60-70mA)

• Board Dimensions: Approximately 26 mm x 20 mm x 2 mm

• Connection Type: Solder Pads (B-, B1, B2, B3, B4)

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Please note, a delivery fee of €4.99 applies for orders under €50. For those in remote areas, be aware that our couriers may apply an extra surcharge. This additional fee helps cover the costs of transporting your items to harder-to-reach locations.