LG F2100 Replacement Battery 3.7V 850mAh 050314Y-NN

LG F2100 / G220 — 3.7V Li-ion Replacement Battery (050314Y-NN)

This is a 3.7V, 850mAh Li-ion cell that replaces part number 050314Y-NN in the LG F2100 and G220 handsets. Both are compact flip phones requiring a slim cell within a 69.67 × 45.96 × 7.28mm envelope. Capacity is 3.15Wh — identical to the original specification.

• F2100 and G220 compatibility: Both models share the same battery bay dimensions, connector pinout, and 3.7V nominal rail. The BMS handshake on each expects the same cell impedance profile, so one part number covers both handsets without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the F2100 platform. The BMS accepted the cell without lockout, charge termination triggered correctly at full voltage, and protection tripped cleanly at the low-voltage cutoff threshold.
• Fuel gauge recalibration on first use: After fitting this cell, run one complete discharge to auto-off followed by a full uninterrupted charge before normal use. The F2100's fuel gauge IC was calibrated to the old cell's discharge curve — skipping this step causes the percentage counter to jump erratically for the first several cycles.

Why the F2100 reports wrong battery percentage after a cell swap

The fuel gauge IC in the F2100 stores a learned discharge curve from the previous cell. A new 850mAh cell has a slightly different impedance and voltage slope, so the IC's stored data no longer matches what it measures. The result is percentage readings that drift, jump, or stall at a fixed value for long periods. One full discharge-to-shutdown followed by a full charge resets the coulomb counter against the new cell's actual behaviour. After that single cycle, percentage reporting stabilises.

Sudden shutdown at 15–25% on the replacement cell

This happens when the cell voltage drops below what the phone's modem or display load can sustain, even though the fuel gauge still shows charge remaining. A fresh cell with a slightly different internal resistance will hit that voltage cliff at a different state of charge than the original. The BMS cuts power to protect the cell before the gauge catches up. To confirm this is the cause, charge to 100% and check that shutdown only occurs below 3.5V under load — if it does, the gauge just needs one more full cycle to recalibrate its cutoff mapping.