About this replacement
Vivo IQOO 11 Pro — 7.74V Li-Polymer Replacement Battery (B-X9)
This is a 7.74V, 2700mAh (20.9Wh) Li-Polymer replacement battery for the Vivo IQOO 11 Pro smartphone. OEM part number B-X9. It slots directly into the IQOO 11 Pro chassis and connects to the same flex cable and BMS handshake points as the original cell.
- IQOO 11 Pro platform fit: The IQOO 11 Pro uses a dual-cell Li-Polymer pack running a 7.74V nominal rail. The connector pinout, BMS communication lines, and physical cell dimensions match the original B-X9 spec — no adapter or wiring modification needed.
- Bench tested on actual hardware: We ran the B-X9 through charge and discharge cycles on the IQOO 11 Pro mainboard. The BMS accepted the cell on first connection, the charge IC initiated correctly, and the fuel gauge IC began tracking coulomb count from cycle one.
- First-cycle calibration on the IQOO 11 Pro: After installation, disable fast charging for the first full discharge-charge cycle. The fuel gauge IC on the IQOO 11 Pro needs one measured cycle at standard current to map the new cell's discharge curve before FlashCharge pushes high current into an uncalibrated state of charge register.
Sudden shutdown at 20–30% on the IQOO 11 Pro after a cell swap
This happens when the fuel gauge IC is still using the discharge curve from the old, degraded cell. The new cell has a different voltage-versus-capacity slope, so the IC calls 20% remaining when the actual cell voltage is already near its low cutoff under modem and display load. The phone shuts off because the real cell voltage drops below the safe floor — not because the replacement cell is defective. One full discharge down to automatic shutdown followed by a full charge resets the coulomb counter and resolves it.
IQOO 11 Pro not powering on after the replacement battery sat in storage
Li-Polymer cells self-discharge during storage. If the B-X9 cell dropped below approximately 2.5V per cell during transit or shelf time, the BMS enters a lockout state and blocks normal boot. Connect the phone to a wall adapter — not a PC port — and leave it for 15 to 20 minutes without pressing the power button. The charge IC trickle-charges the cell back above the BMS recovery threshold, after which the phone should respond normally. If the screen stays dark past 25 minutes, check that the charger is delivering at least 5V 2A.