Samsung Galaxy W21 5G EB-BF917ABY Replacement Battery 3.88V

Samsung Galaxy Z Fold2 Series — 3.88V Li-Polymer Replacement Battery (EB-BF917ABY)

This is a 3.88V, 1890mAh Li-Polymer cell built to the EB-BF917ABY specification. It fits the Samsung Galaxy W21 5G, Galaxy Z Fold2, and Galaxy Z Fold2 UW 5G, along with several related variants. If your foldable is shutting down early or no longer holding a full charge, this cell replaces the degraded original.

• Foldable form factor compatibility: The Galaxy Z Fold2 line and W21 5G share the same narrow-profile cell bay, voltage rail, and BMS handshake protocol. The EB-BF917ABY spec covers all variants in this cluster — the connector pinout and BMS communication are identical across the group.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on Z Fold2 hardware. The BMS accepted the cell without fault flags, charge current stepped correctly through the CC/CV phases, and the protection circuit responded normally to load transitions from the foldable display and 5G modem.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC map its coulomb counter against the new cell's actual discharge curve before high-current charging pushes current into an uncalibrated register.

Sudden shutdown at 20–30% on the Galaxy Z Fold2 after a cell swap

The Z Fold2 runs a large foldable OLED panel and a 5G modem simultaneously — both pull hard current spikes. A new cell with an uncalibrated fuel gauge IC will hit a voltage cliff under that combined load well before the displayed percentage reaches zero. The phone's protection circuit reads an instantaneous voltage drop below the cutoff threshold and shuts down, even though the state-of-charge counter still shows charge remaining. One full discharge-charge cycle without fast charging lets the coulomb counter anchor to the real cell capacity, which typically eliminates the early shutdown.

USB-PD fast charge not accepted on the first cycle after replacement

After a cell swap, the charge IC on the Z Fold2 sometimes defaults to standard 5V/2A input on the first charge cycle while it handshakes with the new BMS. This is not a fault with the cell or the charger — the protocol negotiation between the USB-PD controller and the new BMS takes one full cycle to stabilise. Charge the device once to 100% using the standard wired charger without a fast-charge adapter. Fast charging should resume normally from the second cycle onward.