About this replacement
HTC 7 Pro / T7576 — 3.7V Li-ion Replacement Battery (35H00123-29M)
This is a 3.7V, 2200mAh Li-ion replacement battery for the HTC 7 Pro and T7576 smartphones. It replaces OEM part numbers 35H00123-29M and BA S550. Fit this when the original cell no longer holds a charge through a normal day of use.
- 7 Pro and T7576 fit confirmed: Both models run the same battery bay dimensions and connector pinout. The BMS handshake uses the same communication protocol across the T7576 variant, so one cell covers both without any modification.
- Bench tested on actual hardware: We ran charge and discharge cycles on the HTC 7 Pro platform. The BMS accepted the cell without triggering overcurrent cutoff, and charge termination fired correctly at 4.2V under CC-CV protocol.
- Fuel gauge recalibration on first cycle: After fitting this cell, disable fast charging and run one full discharge down to automatic shutdown, then charge uninterrupted to 100%. This gives the fuel gauge IC a complete discharge curve to map against the new cell — skipping this step is the main reason percentage readings drift or jump after a swap.
Why the HTC 7 Pro reports wrong battery percentage after a cell swap
The 7 Pro uses a coulomb counter that was trained on the original cell's discharge curve over hundreds of cycles. When you fit a new cell, that curve no longer matches the stored data. The fuel gauge IC reads state-of-charge against the old model, so it can report 40% while the cell is closer to 15%. One full uninterrupted discharge-to-shutdown followed by a full charge resets the reference curve and brings percentage readings back in line.
Sudden shutdown at 20–30% on the replacement cell
This happens when the modem or display draws a current spike that drops cell voltage below the BMS cutoff threshold — even though the fuel gauge still shows charge remaining. A fresh cell with an uncalibrated fuel gauge IC is most vulnerable during the first few cycles because the low-voltage floor hasn't been mapped yet. It is not a faulty cell. Run two full discharge-charge cycles without fast charging and the shutdowns will stop as the gauge recalibrates. If shutdown persists past three full cycles, check that cell voltage at rest reads above 3.6V before use.