Sony Ericsson Xperia SO04 Replacement Battery 3.7V 1500mAh

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

This is a 3.7V, 1500mAh Li-ion replacement battery for the NTT DoCoMo XperiaTM (model ASO29038), identified by OEM part number SO04. It slots into the same physical bay as the original cell and connects to the same charge IC and fuel gauge circuit on the motherboard. Capacity listed is from product data: 1500mAh (5.55Wh).

• XperiaTM and ASO29038 fitment: Both models share the SO04 battery footprint — same connector pinout, same BMS communication protocol, and the same 3.7V nominal voltage rail feeding the Snapdragon SoC and radio modules. Swapping between these two devices does not require a different cell.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the XperiaTM platform. The BMS accepted the handshake without fault codes, the charge IC ramped to full current without thermal events, and the fuel gauge IC tracked state-of-charge across the full discharge curve.
• First-cycle fast charge caution: On first use after installation, disable fast charging and run one complete discharge-charge cycle at standard rate. This lets the fuel gauge IC build an accurate discharge curve map against the new cell before high-current charging pushes into an uncalibrated state-of-charge register.

Sudden shutdown at 20–30% on the replacement cell

This is a voltage cliff issue, not a capacity defect. When the modem fires at full transmit power or the display spikes brightness, the instantaneous current draw pulls the cell voltage below the BMS cutoff threshold — even though the fuel gauge still reads 20–30%. The fuel gauge IC is still calibrated to the old cell's impedance curve, so the percentage shown does not match real remaining capacity. One full discharge-to-shutdown followed by a complete charge cycle lets the coulomb counter re-anchor to the new cell's actual curve. After that cycle, the percentage and the real voltage floor re-align.

Device not powering on after the replacement battery sat in storage

Li-ion cells shipped or stored at low state-of-charge can drop below 2.5V per cell, which triggers BMS lockout — the protection circuit opens and blocks all current flow to prevent damage. The phone will show no response to the power button and may not register on the charger at all. Connect to a wall charger rather than a USB port; wall chargers supply enough current to nudge the BMS recovery circuit back into normal mode. Hold the charge connection for at least 15–20 minutes before attempting to power on — by that point the cell should have recovered past the 3.0V re-enable threshold.