HTC U12+ B2Q55100 Replacement Battery 3.85V 3400mAh

HTC U12+ / Exodus 1 — 3.85V Li-Polymer Replacement Battery (B2Q55100)

This 3.85V, 3400mAh Li-Polymer cell replaces part number B2Q55100 in the HTC U12+, U12 Plus, and Exodus 1. It fits the original battery bay and connects to the same charge IC used by HTC's stock cell. Capacity is rated at 13.09Wh from the manufacturer specification.

• U12+, U12 Plus, and Exodus 1 compatibility: These models share the same battery bay dimensions, 3.85V nominal voltage rail, and B2Q55100 connector footprint. The BMS handshake between the charge IC and this cell matches the stock configuration, so the charge profile runs normally without firmware complaints.
• Bench tested on actual hardware: We cycled this cell on the U12+ charge IC and monitored BMS cutoff behaviour at both the low-voltage floor and top-of-charge ceiling. The protection circuit triggered correctly at each threshold, and the charge IC accepted the cell without throwing a charging error on the status bar.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC recalibrate against the new cell's discharge curve before high-current charging pushes current into an uncalibrated cell. Skip this step and the percentage readout will drift for several cycles.

Sudden shutdown at 20–30% on a freshly swapped U12+ cell

The HTC U12+ uses a coulomb counter that was calibrated to the discharge curve of the original cell. A new cell has a slightly different voltage-to-capacity curve, so the fuel gauge underestimates remaining charge near the bottom of the range. When the modem fires up for a call or the display peaks brightness, current draw spikes and the actual cell voltage dips below the BMS cutoff threshold — even though the OS shows 25% remaining. Run one full discharge down to automatic shutdown, then charge uninterrupted to 100% without fast charging. That single cycle writes a new reference curve to the fuel gauge IC and moves the cutoff point back into alignment.

USB-PD fast charge not recognised on first cycle after replacement

After a cell swap, the U12+'s charge IC sometimes defaults to standard 5V/1A input and ignores the USB-PD handshake until it completes one baseline charge at slow rate. This happens because the BMS on the new cell has not yet exchanged a full authentication sequence with the phone's charge controller. Plug into the original HTC charger — not a third-party USB-PD adapter — and let the first charge complete at whatever rate the phone accepts. Once that cycle finishes, fast charging typically re-engages on the second connection without any further steps.