HTC U12 B2Q5W100 Replacement Battery 3.85V 2900mAh

HTC U12 / Desire 12+ Series — 3.85V Li-Polymer Replacement Battery (B2Q5W100)

This is a 3.85V, 2900mAh Li-Polymer replacement battery for the HTC U12, Desire 12+, and Breeze Plus. It uses OEM part number B2Q5W100 and fits the same battery bay without modification. The cell measures 78.60 × 62.78 × 3.48mm — verify yours before ordering if the phone has been previously repaired.

• U12 and Desire 12+ platform fit: Both devices share the same voltage rail, connector pinout, and BMS handshake profile under B2Q5W100. The same charge IC and fuel gauge logic applies across this model family, so one cell covers all four listed variants.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on U12 hardware. The BMS accepted the new cell without error flags, and the charge IC applied the correct CC/CV profile at 3.85V nominal. No thermal anomalies were recorded during the test runs.
• First-cycle fuel gauge recalibration: After installation, disable fast charging and run one full discharge-to-charge cycle at standard current. This lets the fuel gauge IC map its coulomb counter against the new cell's actual discharge curve before high-current charging begins on an uncalibrated cell.

Sudden shutdown at 20–30% on the HTC U12 after a cell swap

This happens because the fuel gauge IC still holds the discharge curve of the old, degraded cell. The new cell has a steeper voltage cliff at low state-of-charge, and the IC miscalculates remaining capacity until it is recalibrated. Under modem or display load, the cell voltage drops below the BMS cutoff threshold while the OS still shows 20–30% remaining. One full discharge down to automatic shutdown, followed by a full charge without interruption, resets the coulomb counter and stops the spurious cutoffs.

USB-PD fast charge not activating on the first cycle after replacement

On the first charge cycle, the HTC charge IC runs a trickle current check against the new cell's impedance before it negotiates the fast-charge protocol. If the cell arrives from storage at low voltage, the IC stays in pre-charge mode and USB-PD handshake does not complete — the phone charges slowly or shows the standard charge icon instead of the fast-charge indicator. Let the first cycle complete fully on a standard 5V charge. From the second cycle onward, fast charging activates normally once the IC has confirmed the cell is above the 3.0V pre-charge exit threshold.