Sony Ericsson Xperia S BA800 Compatible Battery 3.7V 1500mAh

Sony Ericsson Xperia S / LT26i — 3.7V Li-ion Replacement Battery (BA800)

This is a 3.7V, 1500mAh Li-ion replacement battery for the Sony Ericsson Xperia S smartphone, OEM part number BA800. It fits the LT26 and LT26i hardware revisions along with the Arc HD and 14 additional Xperia variants that share the same BA800 footprint. Voltage and cell dimensions match the original spec exactly: 56.80 × 52.90 × 5.10mm.

• LT26 / LT26i platform compatibility: All LT26-series boards run the same 3.7V power rail and use an identical connector pinout and BMS handshake protocol. That is why the BA800 spans the Xperia S, Arc HD, and related variants without modification.
• Bench tested on actual hardware: We cycled this cell on an LT26i unit and confirmed the BMS accepted the charge handshake on the first connection. Charge current ramped correctly through CC and CV phases with no fault flags thrown by the charge IC.
• Fuel gauge recalibration on first use: On first use after installation, run one full discharge-to-charge cycle with fast charging disabled. This lets the fuel gauge IC map its coulomb counter against the new cell's actual discharge curve before high-current charging is applied to an uncalibrated cell.

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

The Xperia S shuts down mid-use at 20–30% because the fuel gauge IC is still using the old cell's discharge curve after replacement. When the modem fires a transmission burst or the display peaks in brightness, the new cell experiences a voltage dip the uncalibrated gauge did not predict. The processor interprets that dip as a critical undervoltage event and cuts power before the gauge reads zero. One complete discharge-charge cycle forces the coulomb counter to relearn the new cell's voltage-versus-capacity relationship and eliminates most of these early shutdowns.

Phone warm near the battery compartment during the first charge after installation

A fresh BA800 cell leaves the warehouse with higher internal impedance than a conditioned cell. On the first charge cycle, the charge IC pushes current into that higher-impedance cell, and the resistance converts some of that energy directly to heat. This is normal and typically resolves after two to three full cycles as the cell's internal impedance drops. If warmth persists beyond the third cycle or the phone becomes hot to the touch, check that no third-party fast-charge adapter is forcing current above the LT26i's rated charge rate of 5V/1A.