Sony Ericsson Xperia SO04 Replacement Battery 3.7V 2600mAh

NTT DoCoMo XperiaTM — 3.7V Li-ion Replacement Battery (SO04)

This 3.7V 2600mAh Li-ion cell replaces the original battery in the NTT DoCoMo XperiaTM (ASO29038). It fits the SO04 variant sold through the NTT DoCoMo network in Japan. Swap it in when the original cell can no longer hold a usable charge through a full day of calls, data, and screen time.

• SO04 platform fit: The XperiaTM SO04 uses a fixed connector layout and a BMS handshake tied to the 3.7V nominal rail. This cell matches that voltage, connector pitch, and physical footprint — 54.49 × 43.62 × 10.46mm — so the phone's charge IC accepts it without a firmware flag.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on an SO04-compatible test rig. The BMS accepted the cell, thermal cutoff did not trigger during the charge phase, and the protection circuit responded correctly at low-voltage cutoff.
• First-cycle fast charge setting: On first use after installation, disable fast charging for one complete discharge-charge cycle. The fuel gauge IC needs to map the new cell's discharge curve before high-current charging is applied to an uncalibrated cell. Re-enable fast charging after that first full cycle completes.

Sudden shutdown at 20–30% on the replacement cell

The XperiaTM SO04's fuel gauge IC holds a discharge curve from the original cell. A fresh 2600mAh cell has a different impedance profile, so the IC misreads the actual state of charge. When the modem fires a high-current burst — during a call or LTE handoff — the reported 25% can represent a voltage that collapses under load. The phone shuts down before the display percentage hits zero. One full discharge-to-cutoff followed by a full charge resets the coulomb counter and corrects the curve.

Phone not powering on after the battery sat in storage

Li-ion cells self-discharge during storage. If the cell voltage drops below 2.5V, the BMS enters a lockout state and the phone will not respond to a normal charger. Connect the device to a low-current USB source — a standard 5V/500mA USB-A port works — and leave it for 20 to 40 minutes without pressing the power button. The BMS trickle-charges out of lockout, then normal charging resumes. Once the phone shows a charge indicator, switch to your standard charger.