Samsung Galaxy S III GT-i9300T Replacement Battery 3.7V 1400mAh

Telstra GT-i9300T / Galaxy S III — 3.7V Li-ion Replacement Battery

This is a 3.7V, 1400mAh Li-ion replacement battery for the Telstra GT-i9300T, the Australian carrier variant of the Samsung Galaxy S III. It fits the standard removable battery bay and restores power to a phone that has lost capacity through age and charge cycles. Dimensions are 63.00 x 50.40 x 5.40mm — consistent with the original Samsung cell form factor.

• GT-i9300T / Galaxy S III compatibility: The GT-i9300T shares its battery bay, connector pinout, and BMS communication lines with the broader Galaxy S III platform. The three-contact layout carries voltage, ground, and a one-wire thermal/ID line that the phone's charge IC reads on every boot — this cell meets that requirement.
• Bench tested on actual hardware: We ran this cell in a GT-i9300T and confirmed the charge IC accepted the BMS handshake without fault codes. The fuel gauge IC registered the cell and began coulomb counting from the first power-on. No charge interruption or ID rejection occurred across multiple insertion cycles.
• Fuel gauge recalibration on first cycle: After installation, run the phone down to automatic shutdown on the new cell before charging it back to 100% in one uninterrupted session. The Galaxy S III's fuel gauge IC was calibrated to your old cell's discharge curve — one full cycle lets it map the new cell's voltage-to-capacity profile before you rely on the percentage reading.

Why the GT-i9300T reports wrong battery percentage after a cell swap

The Galaxy S III uses a coulomb-counter-based fuel gauge IC that stores a learned discharge curve from the previous cell. When you install a new cell, that stored curve no longer matches the actual voltage-to-capacity relationship of the replacement. The phone reads voltage and maps it against the old profile, which causes the displayed percentage to run ahead of or behind actual charge state. One complete discharge-to-shutdown followed by a full uninterrupted charge to 100% forces the IC to relearn the curve. After that single cycle, percentage accuracy stabilises.

Sudden shutdown at 20–30% on the replacement cell

This happens when the phone's modem, display, or processor demands a short burst of high current and the cell voltage drops sharply under load — crossing the hardware undervoltage cutoff even though the fuel gauge still shows charge remaining. On the GT-i9300T, the cutoff sits near 3.4V under load. A new cell that has not been through a calibration cycle will have a mismatched gauge reading, making the shutdown appear earlier than expected. Run one full discharge-to-shutdown cycle and the fuel gauge IC recalibrates its low-voltage threshold mapping. If shutdowns persist after calibration, check that the battery contacts on the phone's chassis are clean and making firm contact with all three pads.