T-Mobile HD7 Replacement Battery BA S460 3.7V 2100mAh

T-Mobile HD7 — 3.7V Li-ion Replacement Battery (BA S460)

This is a 3.7V, 2100mAh Li-ion replacement battery for the T-Mobile HD7 Windows smartphone. It fits the HD7 directly and matches the original cell format, connector, and BMS handshake. OEM part numbers BA S460, BD29100, and 35H00143-01M all cross to this cell.

• HD7 platform fit: The HD7 uses a single-cell 3.7V Li-ion pack with a proprietary connector pinout that carries both power and BMS data lines. This replacement replicates that pinout so the phone's charge IC and fuel gauge IC communicate correctly with the new cell from the first boot.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the HD7 platform and confirmed the BMS handshake completes at power-on, charge termination triggers at the correct voltage ceiling, and the protection circuit cuts current correctly at the low-voltage floor.
• Fuel gauge recalibration on first use: After installation, run one complete discharge down to auto-shutoff, then charge uninterrupted to 100% before normal use. The HD7's fuel gauge IC is calibrated to the old cell's discharge curve — skipping this step causes erratic percentage readings in the first few days.

Why the HD7 reports wrong battery percentage after a cell swap

The HD7 uses a coulomb-counting fuel gauge IC that builds its capacity model over charge cycles. When the original degraded cell is replaced, the IC still references its old discharge curve — so it maps the new cell's higher capacity against incorrect baseline data. This produces percentage readings that jump or stall, typically between 40% and 80%. One full uninterrupted discharge-to-charge cycle gives the IC enough data to rebuild an accurate model against the new cell. After that cycle, percentage tracking stabilises.

Sudden shutdown at 20–30% on the replacement cell

This happens when the cell voltage drops sharply under the combined load of the modem radio and screen backlight — a voltage cliff the fuel gauge did not anticipate. The HD7's processor draws a surge when the modem registers to the network, and a cell that hasn't fully recalibrated can't sustain voltage under that spike. The BMS interprets the voltage drop as a critically low-cell condition and cuts power before the displayed percentage reaches zero. Run the full recalibration cycle first; if shutdowns persist, check that cell voltage at the contacts reads at least 3.6V under screen-on load using a multimeter at the battery terminals.