Sony Xperia 1 II 5G Replacement Battery 3.85V 3850mAh

Sony Xperia 1 II / Xperia 5 II 5G — 3.85V Li-Polymer Replacement Battery (SNYSU54)

This 3.85V, 3850mAh Li-Polymer cell replaces the original SNYSU54 battery in the Sony Xperia 1 II 5G Green Edition, Xperia 5 II 5G, XQ-AS7, and PDX-206. It restores power to the processor, display, camera array, and 5G modem when the original cell degrades or fails. Capacity is 14.82Wh — matching the OEM specification.

• Xperia 1 II and 5 II platform fit: Both handsets share the same PDX-series board layout, battery connector pinout, and BMS communication protocol — which is why a single SNYSU54 cell covers both lines. Voltage rail, physical footprint at 75.65 × 60.85 × 4.70mm, and NTC thermistor position are identical across the group.
• Bench tested on actual hardware: We cycled this cell on a PDX-206 unit and confirmed BMS handshake, charge acceptance across CC and CV phases, and clean cutoff at the 4.35V upper limit. Thermal behaviour stayed within expected range throughout.
• Fuel gauge recalibration on first use: After installation, disable fast charging and run one complete discharge-to-charge cycle at standard rate. The Xperia's fuel gauge IC is calibrated to the old cell's discharge curve — without a slow recalibration pass, the coulomb counter will read against stale data and report inaccurate percentages from the first charge onward.

Sudden shutdown at 20–30% on the Xperia 1 II after a cell swap

This is a voltage cliff issue, not a capacity fault. Under peak load — 5G modem handoff, 4K display refresh, or camera burst — the cell must sustain voltage above the BMS cutoff threshold. A new cell whose fuel gauge IC hasn't completed a full calibration cycle reports a higher state-of-charge than actual terminal voltage can support under that load. The BMS reads the voltage drop as a critical event and shuts the device down to protect the circuit. Run one full discharge-to-charge cycle without fast charging to synchronise the coulomb counter to the new cell's real discharge curve.

USB-PD fast charging not activating after battery replacement

On the first charge cycle after a cell swap, the Xperia charge IC sometimes refuses to negotiate the USB-PD fast charge contract because it detects an uncalibrated cell. This is a protective behaviour — the charge IC won't push high current into a cell whose impedance profile it hasn't mapped. Connect to a standard 5V charger and allow the first full cycle to complete at base rate. After that cycle, USB-PD fast charging should resume normally on subsequent connections.