About this replacement
HTC Desire 728 — 3.8V Li-Polymer Replacement Battery (35H00249-00M)
This is a 3.8V, 2800mAh Li-Polymer replacement battery for the HTC Desire 728 smartphone, including the D728, D728w, and D728t variants. It matches OEM part numbers 35H00249-00M and 35H00249-02M. Install it when the original cell no longer holds a usable charge through a normal day.
- Desire 728 variant compatibility: The D728, D728w, and D728t share the same battery bay dimensions, connector pinout, and BMS handshake protocol — all variants accept this cell without modification.
- Bench tested on actual hardware: We cycled this cell on a Desire 728 unit and confirmed the BMS accepted the cell, reported state-of-charge correctly after calibration, and held voltage above 3.5V under sustained screen and modem load.
- First-cycle fuel gauge recalibration: On first use after installation, disable fast charging and complete one full discharge-charge cycle. This lets the fuel gauge IC map the new cell's discharge curve before fast-charge current is applied to an uncalibrated cell.
Sudden shutdown at 20–30% on the Desire 728 after a cell swap
This is a voltage cliff problem, not a capacity problem. When the modem and screen pull current simultaneously, a new cell with an uncalibrated fuel gauge IC can drop below the 3.4V protection threshold faster than the OS expects. The phone cuts power before the displayed percentage reaches zero. One full discharge-charge cycle — draining to auto-shutoff, then charging uninterrupted to 100% — resets the coulomb counter and eliminates the premature cutoff on most units.
Percentage jumping erratically after fitting the replacement cell
The Desire 728's fuel gauge IC retains the discharge curve from the old cell in its register. When a new cell goes in, the stored curve no longer matches actual cell voltage, so the reported percentage swings as the IC tries to reconcile real voltage readings against stale data. The fix is straightforward: drain the phone to auto-shutoff, then charge to 100% without interruption. After one complete cycle the IC overwrites the old curve and percentage readings stabilise. Check that the percentage holds steady at a consistent load — screen on, Wi-Fi active — before trusting the reading.