T-Mobile SGH-T999V Galaxy S III Replacement Battery 3.8V 2100mAh

T-Mobile SGH-T999V Galaxy S III — 3.8V Li-ion 2100mAh Replacement Battery

This 3.8V Li-ion cell replaces the original battery in the T-Mobile Samsung Galaxy S III (SGH-T999V). It fits the SGH-T999V and covers the broader Galaxy S3 lineup that shares the same battery bay and connector. Capacity is 2100mAh (7.98Wh), matching the stock specification.

• SGH-T999V and Galaxy S III platform fit: These models share an identical battery bay, contact pitch, and NTC thermistor line. The same cell works across all variants because the charge IC reads the same thermistor resistance curve regardless of carrier branding.
• Bench tested on actual hardware: We ran this cell through a full charge cycle on the SGH-T999V. The charge IC accepted the cell without error flags, the BMS reported temperature within normal range, and the fuel gauge initialised correctly at first boot.
• Fuel gauge recalibration on first use: After installing this battery, disable fast charging and run one complete discharge-charge cycle at standard rate. This allows the coulomb counter to map the new cell's discharge curve before high-current charging pushes current into an uncalibrated state.

Sudden shutdown at 20–30% on the SGH-T999V after a cell swap

The Galaxy S III's fuel gauge IC stores a learned discharge curve from the previous cell. A new cell with a slightly different internal resistance profile causes the IC to misread remaining capacity. When the modem fires a high-power transmission burst or the display hits full brightness, voltage drops sharply under load. The IC sees the voltage cliff and triggers an emergency shutdown even though the reported percentage looks safe. One full discharge-charge cycle at standard rate resets the learned curve and stops the premature cutoffs.

OS showing erratic or jumping battery percentage after replacement

Percentage jumping — say, 45% dropping to 12% in seconds — points to the coulomb counter still running the old cell's charge model. The SGH-T999V uses a software-tracked fuel gauge that does not auto-reset when the physical cell changes. Drain the battery until the phone shuts off on its own, then charge uninterrupted to 100% without removing the cable. After that single calibration cycle, percentage readings stabilise and track accurately against the new cell's actual capacity.