Samsung Galaxy S II Replacement Battery EB-F1A2GBU 3.7V 2600mAh

Samsung Galaxy S II GT-I9100 — 3.7V Li-ion Replacement Battery (EB-F1A2GBU)

This is a 3.7V, 2600mAh lithium-ion battery for the Samsung Galaxy S II (GT-I9100). It replaces OEM part numbers EB-F1A2GBU, EB-FLA2GBU, and EB-L102GBK. If your original cell no longer holds charge or shuts down unexpectedly under load, this is a direct cell swap.

• GT-I9100 cell compatibility: The Galaxy S II uses a removable single-cell Li-ion pack with a 3.7V nominal rail and a three-contact connector carrying voltage, ground, and a thermistor line. All three OEM part numbers listed share that contact layout, so the swap is mechanical and electrical like-for-like.
• Bench tested on actual hardware: We ran this cell on a GT-I9100 and confirmed the BMS communicates correctly with the fuel gauge IC — charge current ramps up normally from trickle, transitions to CC, then drops to CV without error flags in the charging log.
• Fuel gauge recalibration after install: On first use, disable any fast-charge accessories and run one full discharge-to-charge cycle at standard current. This lets the fuel gauge IC learn the new cell's discharge curve before it begins reporting percentages — skipping this step produces erratic percentage readings for several days.

Sudden shutdown at 20–30% on the GT-I9100 after a cell swap

The Galaxy S II's fuel gauge IC stores a discharge curve from the original cell in non-volatile memory. When a new cell goes in, the IC applies the old curve — and if the new cell has a steeper voltage drop under modem or display load, the phone hits a low-voltage cutoff before the percentage readout reaches zero. The BMS trips at approximately 3.0V per cell to protect the chemistry. One full uninterrupted discharge and recharge cycle forces the coulomb counter to reset and map the actual curve of the new cell.

Phone warm near the battery compartment on the first charge cycle

A new cell arrives with higher internal impedance than a cell that has been through several cycles. The charge IC on the GT-I9100 pushes standard current into that higher-impedance cell, and the extra resistive heating is normal for the first one or two charges. Surface temperature should stabilise below 40°C as internal impedance drops with cycling. If the back cover stays hot beyond the second full charge, check that the thermistor contact on the battery connector is seated flush — a lifted contact removes thermal feedback from the charge circuit entirely.