About this replacement
HTC U20 5G / F233 — 3.85V Li-Polymer Replacement Battery (B2Q9F100)
This is a 3.85V, 4650mAh (17.9Wh) Li-Polymer cell built to replace the original B2Q9F100 battery in the HTC U20 5G and F233. It slots into the same footprint at 83.80 × 65.06 × 5.16mm and connects to the same BMS handshake the phone expects. When the stock cell degrades and can no longer hold voltage under modem or display load, this cell restores full operating capacity.
- U20 5G and F233 fit: Both models share the B2Q9F100 form factor, connector pinout, and BMS communication protocol. The fuel gauge IC on this platform reads cell data over a single-wire interface — the replacement cell carries the same register map so the phone accepts it without flagging a battery error.
- Bench tested on actual hardware: We cycled this cell through charge and load on the U20 5G platform. The BMS accepted the charge handshake on the first connect, current tapered correctly at end-of-charge, and the protection circuit tripped cleanly on a simulated over-discharge event at 2.5V per cell.
- Fuel gauge recalibration on first use: On first use after installation, disable fast charging and run one full discharge-charge cycle at standard rate. This lets the coulomb counter recalibrate its state-of-charge model against the new cell's actual discharge curve before high-current charging runs into an uncalibrated gauge.
Sudden shutdown at 20–30% on the HTC U20 5G after a cell swap
The U20 5G's processor and 5G modem pull a sharp current spike when switching between sub-6GHz bands or waking from deep sleep. If the fuel gauge IC is still calibrated to the old cell's internal resistance curve, it reads terminal voltage incorrectly under that load spike. The phone sees a voltage cliff — the cell voltage drops briefly below the shutdown threshold even though the cell itself has charge remaining. One full slow discharge-charge cycle after fitting the new cell resets the coulomb counter and eliminates most of these early shutdowns.
USB-PD fast charge not activating on the first cycle after replacement
After fitting a new cell, the charge IC on the U20 5G sometimes defaults to trickle current on the first plug-in while it re-evaluates BMS state. This is a protection behaviour — the IC waits for a valid cell voltage reading above approximately 3.0V before stepping up to the negotiated USB-PD rate. If the phone charges slowly on the first cable connection, unplug, wait 30 seconds, and reconnect. By the second or third connection the IC steps up to full fast-charge current as expected.