Samsung Galaxy Z Fold4 EB-BF937ABY Replacement Battery 3.88V 2200mAh

Samsung Galaxy Z Fold4 — 3.88V Li-Polymer Replacement Battery (EB-BF937ABY)

This is a 3.88V, 2200mAh Li-Polymer replacement cell for the Samsung Galaxy Z Fold4. It fits the sub-battery position in the dual-cell configuration used across SM-F936J, SM-W9023, W23 5G, and related variants. Capacity is 2200mAh (8.54Wh), matching the OEM specification for this cell position.

• Dual-cell architecture across Z Fold4 variants: Samsung splits the Fold4's power system across two physically separate cells to fit the folding form factor. This battery covers the sub-cell (EB-BF937ABY). All listed SM-F936J, SM-W9023, and W23 5G models share the same connector pinout, BMS handshake voltage, and cell dimensions — that's why they share this part.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on a Z Fold4 board. The BMS accepted the cell without fault flags, and the charge IC stepped through trickle, CC, and CV phases cleanly. No thermal events at rated charge current.
• Fuel gauge recalibration on first cycle: On first use after installation, disable fast charging and run one complete discharge-to-charge cycle. The fuel gauge IC recalibrates its coulomb counter against the new cell's actual discharge curve. Skipping this step is the single most common reason the percentage readout drifts or jumps after a cell swap.

Why the Z Fold4 reports wrong battery percentage after a cell swap

Samsung's fuel gauge IC builds a learned model of each cell's voltage-to-capacity curve over many cycles. When a new cell goes in, that model no longer matches physical reality. The IC will read voltage correctly but map it to the wrong state-of-charge percentage until it recalibrates. One full discharge below 5% followed by a complete charge to 100% — with fast charging off — gives the coulomb counter enough data to relearn the new curve. After that cycle, percentage accuracy normalises.

Sudden shutdown at 20–30% remaining on the replacement cell

This happens when the fuel gauge IC is still using stale calibration data from the old cell. Under heavy load — 5G modem active, inner display at full brightness — the new cell's voltage drops faster than the IC expects, hitting the hardware cutoff threshold before the percentage display reaches zero. The device sees a voltage cliff and shuts down to protect the cell. Run one full recalibration cycle as described above, then verify the shutdown doesn't repeat. If it does after calibration, check that resting voltage at 30% reads above 3.7V with a multimeter — anything below that points to a different fault.