BANNO GT03B Replacement Battery 3.7V 750mAh Li-ion

BANNO GT03B — 3.7V Li-ion Replacement Battery

This is a 3.7V, 750mAh (2.78Wh) lithium-ion cell for the Nokia GT03B mobile phone. It replaces the original battery when the cell has degraded and can no longer hold adequate charge for calls, messaging, and basic functions. Dimensions are 53.00 × 33.90 × 5.70mm — verify these against your existing cell before fitting.

• GT03B platform fit: The Nokia GT03B uses a low-drain battery architecture with a straightforward connector and no multi-pin BMS handshake — voltage rail and physical footprint are the only match criteria for this platform.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on the GT03B platform. The BMS accepted charge from a standard 5V USB source without cutoff events, and voltage held steady through the discharge curve above the 3.0V floor.
• Fuel gauge recalibration on first cycle: On first use after installation, run one complete discharge down to the auto-shutoff threshold, then charge to 100% without interruption — this lets the phone's fuel gauge IC map its algorithm to the new cell's actual discharge curve before reporting percentages.

Why the GT03B reports wrong battery percentage after a cell swap

The GT03B tracks charge state using a fuel gauge IC that builds its reference curve from historical cell behaviour. When you fit a new cell, that curve no longer matches the actual chemistry, so percentage readings drift or jump. The IC needs one full uninterrupted discharge-to-shutoff and recharge cycle to reset its internal model. Until that cycle completes, readings between 30% and 70% are likely to be inaccurate.

Sudden shutdown at 20–30% on the replacement cell

This happens when the fuel gauge IC is still calibrated to a worn cell's voltage curve. The old cell may have held voltage under screen and modem load down to a low state of charge — a fresh cell with a steeper voltage cliff hits the BMS undervoltage cutoff earlier than the gauge predicts. The phone shuts down at what the OS thinks is 20–30%, but the cell has already dropped below the safe floor under momentary load. Run one full discharge cycle to 0% auto-shutoff and recharge to 100% to correct the calibration.