Telstra F480 Replacement Battery 3.7V 850mAh Li-ion

Telstra F480 / F480T — 3.7V Li-ion Replacement Battery

This is a 3.7V 850mAh Li-ion replacement battery for the Telstra F480 and F480T mobile phones. It slots into the original battery bay and restores power to these early-2000s handsets. Capacity is 850mAh — matching the original cell specification.

• F480 and F480T compatibility: Both models share the same battery bay dimensions, voltage rail, and connector pinout. One cell covers both variants — no hardware modification needed.
• Bench tested on actual hardware: We ran a full discharge-charge cycle on the F480 platform. The BMS accepted the cell on first insertion, and the charge IC engaged normally without throwing a fault state.
• Fuel gauge recalibration on first cycle: After installing this cell, run one complete discharge down to automatic shutoff, then charge to 100% without interruption. The F480's fuel gauge IC is calibrated to the old cell's discharge curve — skipping this step causes erratic percentage readings from the first day of use.

Why the F480 reports wrong battery percentage after a cell swap

The F480 uses a fuel gauge IC that tracks charge state against a stored discharge curve from the previous cell. A new cell has a different internal impedance profile, so the IC's stored curve no longer matches real voltage behaviour. The result is percentage readings that jump around or stall at values like 40% before the phone cuts off. One full discharge-charge cycle rewrites the reference curve and brings the percentage display back in line with actual charge state.

Sudden shutdown at 20–30% on the replacement cell

This happens when the cell voltage drops below the BMS cutoff threshold under load — even though the fuel gauge still shows charge remaining. On the F480, the display backlight and call radio pulling current simultaneously can cause a brief voltage sag that triggers the protection circuit. It is most common in the first few cycles before the fuel gauge IC recalibrates. Run one full cycle and check that resting voltage reads above 3.6V before the next use.