T-Mobile SDA II Music Replacement Battery 3.7V 2200mAh

T-Mobile SDA II Music — 3.7V Li-ion Replacement Battery

This is a 3.7V, 2200mAh Li-ion cell that fits the T-Mobile SDA II Music and the broader SDA family — including the SDA, SDA II, and SDA US. It replaces the original battery when capacity has dropped or the cell no longer holds a charge. Voltage and form factor match the original T-Mobile spec.

• SDA family compatibility: The SDA, SDA II, SDA II Music, and SDA US all run on the same 3.7V single-cell Li-ion platform with a shared connector and BMS handshake. One cell revision covers the entire lineup without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the SDA platform. The BMS accepted the cell without fault codes, charge termination triggered correctly at 4.2V, and low-voltage cutoff engaged cleanly under load.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging for one complete discharge-charge cycle. This gives the fuel gauge IC time to map the new cell's discharge curve before high-current charging begins on an uncalibrated cell.

Sudden shutdown at 20–30% on the replacement cell

This is a voltage cliff issue, not a capacity defect. When the modem or screen draws peak current, a new uncalibrated cell can sag below the BMS cutoff threshold before the percentage reading reflects actual depletion. The fuel gauge IC is still running the old cell's discharge map, so the reported percentage and the real cell voltage are out of sync. Run one full discharge down to shutdown, then charge to 100% uninterrupted — this resets the coulomb counter against the new cell curve.

Phone warm near the battery during the first few charge cycles

A fresh high-impedance cell generates more heat during the first few charges as the charge IC pushes current into an uncalibrated cell. This is normal behaviour and typically resolves after two or three full cycles. If the device stays warm past the fifth cycle or gets hot to the touch, check that charge current isn't stuck at a high rate due to a firmware state from the previous battery. A full power-off restart between the first and second charge often clears this.