HB5N1 T-Mobile myTouch Replacement Battery 3.7V 1500mAh

T-Mobile myTouch Series — 3.7V Li-ion Replacement Battery (HB5N1)

This is a 3.7V, 1500mAh Li-ion battery for the T-Mobile myTouch and myTouch Q lineup, including the myTouch Q U8730 and myTouch U8680. It replaces the OEM HB5N1 and HB5N1H cells. Fit the physical footprint at 51.30 × 50.80 × 5.60mm — confirm before ordering if your variant isn't listed.

• myTouch and myTouch Q compatibility: The U8680 and U8730 share the same battery bay dimensions, connector pinout, and BMS handshake protocol. Both accept the HB5N1 cell without modification to the contact plate or housing.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on the myTouch platform. The BMS engaged charge termination correctly at 4.2V and held low-voltage cutoff at the expected floor — no erratic shutdowns observed during the test sequence.
• First-cycle fuel gauge reset: After installing this battery, run one complete discharge to automatic shutdown, then charge uninterrupted to 100% before normal use. This lets the phone's fuel gauge IC map the new cell's discharge curve before it starts reporting state-of-charge to the OS.

Why the myTouch reports wrong battery percentage after a cell swap

The fuel gauge IC in the myTouch stores a learned discharge curve from the original cell. When a new cell goes in, that stored curve no longer matches actual cell chemistry and impedance. The OS reads the IC's estimate, not the cell voltage directly, so percentages drift — sometimes reading 40% when the phone is near cutoff. One full discharge-charge cycle forces the IC to recalibrate its coulomb counter against the new cell and corrects the reporting.

Sudden shutdown at 20–30% on the replacement cell

This happens when the cell voltage drops sharply under modem or screen load — a voltage cliff the fuel gauge IC didn't predict because it's still calibrated to the old cell. The phone's protection circuit cuts power before the OS can log a low-battery event, so the shutdown appears instant. It's most common in the first few cycles on a replacement cell. Run two full discharge-to-shutdown cycles and the IC's learned curve will shift to match the new cell's voltage profile, pushing the cutoff point lower.