About this replacement
Samsung Galaxy Z Flip 4 — 3.88V Li-Polymer Replacement Battery (EB-BF723ABY)
This is a 3.88V, 2500mAh Li-Polymer replacement battery for the Samsung Galaxy Z Flip 4 foldable smartphone. It fits SM-F721U, SM-F721U1, SM-F721W, and the wider Z Flip 4 variant lineup. Swap it in when the original cell can no longer hold a usable charge or fails to power the device entirely.
- Z Flip 4 variant compatibility: All SM-F721 sub-variants share the same 3.88V battery bay, flex connector pinout, and BMS handshake. A single cell — EB-BF723ABY — covers the full regional lineup without any hardware modification.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on a Z Flip 4 unit. The BMS accepted the cell on first connection, charge IC ramped normally through CC and CV phases, and protection circuits held cutoff at spec voltage.
- 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 recalibrate its coulomb counter against the new cell's discharge curve before high-current fast charging pushes current into an uncalibrated cell.
Sudden shutdown at 20–30% on the Z Flip 4 after a cell swap
The Z Flip 4 runs a high-resolution foldable display and an always-on modem — both create sharp current spikes. If the fuel gauge IC is still calibrated to the old cell's discharge curve, it misjudges the new cell's actual state of charge. The voltage drops faster than the OS expects under load, and the phone shuts off to protect the BMS even though the reported percentage looks healthy. One full slow-charge cycle resets the coulomb counter and aligns the percentage readout with real cell capacity. After that cycle, shutdowns at 20–30% should stop.
USB-PD fast charging not activating on the first cycle after replacement
On first connection to a fast charger, the Z Flip 4's charge IC runs a handshake with the new BMS to verify the cell is within safe parameters. Some units default to standard 5W charging on that first cycle while the IC collects baseline impedance data from the new cell. This is not a fault — it is the charge IC being cautious with an uncalibrated cell. Plug into a USB-PD charger, let the phone charge fully at whatever rate it accepts, then disconnect and reconnect. Fast charge typically activates from the second cycle onward.