Samsung Galaxy W21 5G EB-BF916ABY Replacement Battery 3.88V 2050mAh

Samsung Galaxy Z Fold2 Series — 3.88V Li-Polymer Replacement Battery (EB-BF916ABY)

This is a 3.88V, 2050mAh Li-Polymer replacement battery for the Samsung Galaxy Z Fold2, Galaxy Z Fold2 UW 5G, Galaxy W21 5G, and compatible models. It uses OEM part number EB-BF916ABY and sits in the outer display half of the foldable chassis. When the original cell degrades, the phone shows rapid capacity loss, erratic percentage readings, or fails to power on.

• Foldable platform compatibility: The Z Fold2 splits power across two cells — an inner and an outer. This cell (EB-BF916ABY) serves the outer display half. All listed models share the same voltage rail, connector pinout, and BMS handshake requirements, which is why they draw from the same part number.
• Bench tested on actual hardware: We ran this cell through charge-discharge cycles on Z Fold2 hardware. The BMS accepted the cell without error flags, stepped through CC/CV phases correctly, and held voltage above 3.5V under combined modem and display load.
• Fuel gauge recalibration after install: On first use after fitting this cell, disable fast charging and run one full discharge-charge cycle at standard rate. The fuel gauge IC in the Z Fold2 is calibrated to the old cell's discharge curve — one slow cycle resets the coulomb counter against the new cell before fast charge current is applied.

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

This is a voltage cliff failure. The new cell's discharge curve doesn't match the profile the fuel gauge IC learned from the old cell, so the reported percentage is ahead of the actual cell voltage. Under a combined load — 5G modem, outer display, and background sync — the cell voltage drops below the BMS cutoff threshold faster than the OS expects. The phone shuts off even though the gauge still shows charge remaining. One full slow discharge-charge cycle forces the coulomb counter to remap the curve. After that cycle, shutdown behaviour typically returns to normal.

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

Samsung's fast charge protocol requires a BMS handshake before the charge IC ramps current. On a brand-new cell, the BMS may not yet have enough charge history to confirm cell health to the charge IC, so it defaults to standard 5W input on the first cycle. This is expected behaviour, not a fault. Let the phone complete one full charge at standard rate. On the second cycle, fast charge re-engages once the BMS has logged a valid baseline cycle.