Samsung Galaxy Z Fold4 EB-BF936ABY Compatible Battery 3.88V 2000mAh

Samsung Galaxy Z Fold4 — 3.88V Li-Polymer Replacement Battery (EB-BF936ABY)

This is a 3.88V, 2000mAh Li-Polymer battery that replaces the EB-BF936ABY cell inside the Samsung Galaxy Z Fold4. It fits SM-F936J, SM-W9023, and W23 5G variants among other Z Fold4 hardware revisions. Capacity is 2000mAh (7.76Wh) — matching the original spec exactly.

• Z Fold4 platform compatibility: All listed SM-F936 and W23 variants share the same battery bay geometry, flex connector pin-out, and BMS handshake protocol. The fuel gauge IC on each of these boards reads the same cell identification registers, so the replacement cell is recognised without any hardware modification.
• Bench tested on actual hardware: We ran this cell through full charge cycles on a Z Fold4 board and confirmed the BMS accepted the cell, charge termination triggered correctly at 4.35V, and the protection circuit tripped cleanly at the low-voltage cutoff threshold without latching.
• Fuel gauge recalibration after install: On first use after installation, disable fast charging and complete one full discharge-charge cycle at standard speed. This gives the fuel gauge IC one clean pass to map the new cell's discharge curve before fast-charge current is applied to an uncalibrated cell.

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

The Z Fold4 uses a coulomb-counter-based fuel gauge IC that builds its state-of-charge model against the previous cell's discharge curve. When a new cell goes in, that learned curve no longer matches the actual voltage-to-capacity relationship of the fresh cell. The gauge will read high early in discharge and then drop sharply as the cell voltage falls through the knee of the curve. One full slow discharge from 100% to automatic shutdown, followed by a full charge, gives the IC enough data to rebuild an accurate curve. After that cycle, the percentage display tracks normally.

Sudden shutdown at 20–30% on the replacement cell

This happens when the fuel gauge IC still holds the old cell's curve in memory and the reported percentage no longer reflects true cell voltage. The display shows 25% while the actual cell voltage has already dropped to near the BMS cutoff threshold — around 3.0V under modem or display load. The Z Fold4's inner and outer displays, 5G modem, and hinge sensors create simultaneous current draws that accelerate voltage sag on an uncalibrated cell. Complete the one full discharge-charge recalibration cycle at slow charge speed, and the gauge will begin calling shutdown at the correct voltage floor.