HTC U11+ Replacement Battery 3.85V 3800mAh 35H00277-00M

HTC U11+ — 3.85V Li-Polymer Replacement Battery (35H00277-00M)

This 3.85V, 3800mAh lithium-polymer cell replaces the original battery in the HTC U11 and U11 Plus smartphones. It matches OEM part numbers 35H00277-00M and 35H00271-01M. Rated at 14.63Wh, it restores full operating capacity to the handset.

• U11 and U11 Plus compatibility: Both handsets share the same battery bay dimensions (76.30 × 63.00 × 4.40mm), connector pinout, and BMS handshake protocol. One cell fits either variant without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on U11 Plus hardware. The BMS accepted the full charge current without tripping cutoff, and the fuel gauge IC tracked state-of-charge accurately by the second full cycle.
• First-cycle fast charge tip: On first use after installation, disable fast charging and run one complete discharge-charge cycle at standard rate. This lets the fuel gauge IC recalibrate against the new cell's discharge curve before high-current charging pushes current into an uncalibrated state.

Sudden shutdown at 20–30% on the U11 Plus after a cell swap

A new cell has a slightly different voltage-discharge curve than the aged cell the fuel gauge IC was calibrated to. When the phone demands high current — modem activity, screen-on bursts — the new cell's voltage drops faster than the IC expects. The IC reads that drop as a critical low-voltage event and triggers an emergency shutdown even though capacity remains. One full discharge-to-cutoff and recharge cycle at standard rate resets the coulomb counter and aligns the IC to the new curve.

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

On the first connection post-install, the BMS in a new cell may not immediately present the expected voltage handshake to the HTC charge IC, causing the phone to fall back to standard 5V charging. This is not a fault — it resolves once the BMS completes its first full charge cycle and the charge IC re-negotiates the protocol. Plug into the original HTC charger rather than a third-party USB-PD adapter for the first cycle. Fast charging should resume normally from the second cycle onward.