HTC Rezound Replacement Battery BTR6425B 3.7V 1150mAh

HTC Rezound / ThunderBolt 2 — 3.7V Li-ion Replacement Battery (BTR6425B)

This is a 3.7V, 1150mAh Li-ion replacement battery for the HTC Rezound, Vigor, ThunderBolt 2, and Droid Incredible HD. It uses OEM part numbers BTR6425B, BTR6425, 35H00168-02M, 35H00168-03M, BH98100, and 35H00168-06M. Swap it in when your original cell no longer holds a charge or causes unexpected shutdowns.

• Rezound / ThunderBolt 2 platform compatibility: These models share the same battery bay dimensions (57 x 44 x 5mm), connector pinout, and BMS handshake protocol — one cell fits all listed variants without modification.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on a Rezound unit. The BMS communicated charge state correctly, cutoff triggers fired at the correct low-voltage threshold, and charge acceptance across the full 1150mAh capacity was confirmed.
• Fuel gauge recalibration on first use: After installing this cell, disable fast charging and run one complete discharge-charge cycle at standard rate. The Rezound's fuel gauge IC is calibrated to the old cell's discharge curve — this single cycle resets it against the new cell before high-current charging is applied.

Why the Rezound reports wrong battery percentage after a cell swap

The Rezound uses a coulomb-counting fuel gauge IC that builds its percentage model from the previous cell's charge curve over many cycles. When you install a new cell, that model is stale — it doesn't match the new cell's actual voltage-to-capacity relationship. The gauge can over- or under-report by 10–20% until it relearns. One full discharge down to automatic cutoff, followed by a full uninterrupted charge, forces the IC to rebuild its lookup table against the replacement cell.

Sudden shutdown at 20–30% charge remaining

This happens when the cell voltage drops sharply under the combined load of the LTE modem, display, and processor — a voltage cliff the fuel gauge didn't predict. The phone reads 25% on the gauge but the actual cell voltage has already dipped below the shutdown threshold under that instantaneous current draw. It is not a defective battery; it is a miscalibrated gauge. Run two full discharge-charge cycles at standard charge rate and confirm the cell rests at 4.15–4.20V at 100% gauge reading before returning to normal use.