F28 Fujitsu Arrows V Replacement Battery 3.7V 1600mAh

Fujitsu Arrows V F-04E — 3.7V Li-ion Replacement Battery (F28)

This 3.7V, 1600mAh Li-ion cell replaces the OEM F28 battery in the Fujitsu Arrows V F-04E and Arrows X F-02E smartphones. It fits the original battery bay without modification and connects to the same BMS contacts as the factory unit. Capacity is 1600mAh (5.92Wh), matching the original specification.

• Arrows V F-04E and Arrows X F-02E compatibility: Both models share the same battery bay dimensions, contact layout, and BMS handshake protocol. The F28 part number covers either device — the voltage rail and connector pitch are identical across the two variants.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on the Arrows V F-04E. The BMS accepted the cell without tripping low-voltage lockout, and the charge IC ramped normally through constant-current and constant-voltage phases.
• Fuel gauge recalibration on first use: On first installation, disable any fast-charge mode and run one complete discharge-to-charge cycle at standard rate. This lets the fuel gauge IC map its coulomb counter to the new cell's actual discharge curve before high-current charging begins on an uncalibrated cell.

Sudden shutdown at 20–30% on the Arrows V F-04E after a cell swap

The Arrows V's fuel gauge IC stores a discharge curve calibrated to the original cell. A new cell with a slightly different internal resistance profile will hit a voltage cliff the gauge doesn't anticipate — the phone reads 25% but the cell voltage under modem or screen load drops below the BMS cutoff threshold. The phone shuts off to protect the cell. One full discharge from 100% to automatic shutdown, followed by a full uninterrupted charge, forces the coulomb counter to relearn the new cell's curve. After that cycle, the reported percentage tracks actual cell voltage accurately under load.

Phone feels warm near the battery compartment during the first charge

A new Li-ion cell has higher internal impedance than a broken-in cell. During the first charge cycle, the charge IC pushes current into a cell with more resistance than it expects, which converts more energy to heat than usual. This is normal on the first one or two cycles and reduces as the cell's impedance settles. If the device stays warm past the second full charge, check that the back cover is fully seated — a gap traps heat against the battery. Measure the phone surface temperature; above 45°C at the cover warrants a longer cool-down before continuing.