T-Mobile Energy HBG7300 Replacement Battery 3.7V 1300mAh

T-Mobile Energy — 3.7V Li-ion Replacement Battery (HBG7300)

This is a 3.7V, 1300mAh Li-ion replacement battery for the T-Mobile Energy smartphone. It uses OEM part number HBG7300 and slots directly into the Energy's battery bay. Capacity is 1300mAh (4.81Wh), matching the original cell specification.

• T-Mobile Energy compatibility: The Energy uses a single-cell Li-ion pack at 3.7V nominal with a connector and BMS handshake specific to this chassis. Swapping to a cell that deviates from this voltage rail causes the fuel gauge IC to report inaccurate percentages from the first boot.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the Energy platform. The BMS accepted the cell without fault codes, and the charge IC completed a full constant-current to constant-voltage taper normally.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging and run one complete discharge-to-charge cycle. This lets the fuel gauge IC map the new cell's discharge curve before the charge IC applies high-current fast charging to an uncalibrated cell.

Why the T-Mobile Energy reports wrong battery percentage after a cell swap

The Energy's fuel gauge IC stores a learned discharge curve from the original cell. When a new cell goes in, that stored curve no longer matches the actual voltage-to-capacity relationship of the replacement. The IC keeps reading against the old curve, so the percentage display drifts. One full discharge and charge cycle forces the coulomb counter to reset and rebuild an accurate model against the new cell.

Sudden shutdown at 20–30% on the replacement cell

This happens when the cell voltage drops below the BMS cutoff threshold under load — typically during modem transmit bursts or screen-on wake events — even though the reported percentage looks healthy. A fresh Li-ion cell with an uncalibrated fuel gauge IC is especially prone to this because the IC cannot accurately predict the voltage cliff. Run one full calibration cycle first: discharge until the phone shuts off on its own, then charge uninterrupted to 100%. After that cycle, unexpected shutoffs above 15% should stop.