Samsung Galaxy Note II SGH-T879 Replacement Battery 3.7V 2500mAh

T-Mobile SGH-T879 Galaxy Note — 3.7V Li-ion Replacement Battery

This is a 3.7V, 2500mAh Li-ion cell for the T-Mobile SGH-T879, which Samsung sold as the Galaxy Note II on T-Mobile's network. It replaces the original cell when the phone shuts down early, charges slowly, or the battery swells inside the chassis. Capacity figures come from the product data — 9.25Wh total energy.

• SGH-T879 and Galaxy Note compatibility: Both names point to the same handset on the same T-Mobile hardware platform. The battery connector, cell dimensions (67.50 × 51.90 × 5.90mm), and BMS communication lines are identical across these variants.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a Galaxy Note II platform. The BMS accepted the charge protocol without flagging an error, and the protection circuit tripped correctly at the low-voltage cutoff threshold.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging and run one complete discharge-charge cycle. This lets the fuel gauge IC map the new cell's discharge curve before the OS starts making percentage estimates against it — skipping this step is the main reason the phone shows erratic percentages after a swap.

Sudden shutdown at 20–30% on the SGH-T879

The SGH-T879 runs a Snapdragon SoC alongside an LTE modem — both draw current spikes that a degraded or freshly installed cell can struggle to sustain. When cell voltage drops below roughly 3.4V under that combined load, the BMS cuts output before the OS can register the actual state of charge. The phone reads 25% but the cell voltage has already hit the protection floor. One full calibration cycle — full charge, full discharge without interruption — lets the coulomb counter reset its end-of-discharge reference point and eliminates most false shutdowns.

OS percentage jumping erratically after cell replacement

Android's fuel gauge IC on the Note II platform stores a learned discharge curve from the previous cell. Drop in a new cell and that stored curve no longer matches the actual voltage-to-capacity relationship of the replacement. The result is percentage readings that jump — often 15 to 20 points — as the IC tries to reconcile real-time voltage against the old model. Fix: charge to 100%, let the phone drain to automatic shutdown without plugging in mid-cycle, then charge back to 100% uninterrupted. After that single cycle the IC recalibrates against the new cell and readings stabilise.