Sony Ericsson Xperia MT27 Replacement Battery AGPB009-A002 3.7V 1260mAh

Sony Ericsson Xperia MT27 Series — 3.7V Li-Polymer Replacement Battery (AGPB009-A002)

This 3.7V, 1260mAh lithium-polymer cell replaces the original AGPB009-A002 battery in the Sony Ericsson Xperia MT27, MT27i, Pepper, and Xperia Sola smartphones. The cell matches the original 66.60 x 32.65 x 4.50mm footprint and connects directly to the stock charge IC and fuel gauge circuit. Capacity is 1260mAh (4.66Wh) — the same rating as the factory cell.

• MT27, MT27i, Pepper, and Xperia Sola compatibility: All four models share the same battery bay dimensions, connector pinout, and BMS handshake protocol. The charge IC on each variant reads cell impedance on the first charge cycle, so the same physical cell works across the group without modification.
• Bench tested on actual hardware: We ran this cell through a full charge-discharge cycle on an MT27i and monitored BMS communication. The protection circuit tripped correctly at low-voltage cutoff, and the charge IC accepted the cell without fault codes.
• Fuel gauge recalibration on first use: After installing this cell, disable fast charging and run one complete discharge down to automatic shutdown, then charge to 100% uninterrupted. This lets the coulomb counter recalibrate against the new cell's actual discharge curve before high-current charging begins.

Why the Xperia MT27 reports wrong battery percentage after a cell swap

The Xperia MT27 uses a coulomb counter tied to the original cell's learned discharge curve. When you swap in a new cell, that learned data no longer matches the physical chemistry inside the phone. The fuel gauge IC keeps using the old curve, so the percentage shown on screen drifts from actual cell state. One full discharge-to-shutdown followed by a full uninterrupted charge resets the learned curve and brings the reported percentage back in line with true capacity.

Sudden shutdown at 20–30% on the replacement cell

This happens when the cell voltage drops below what the modem and display subsystem need under combined load — even though the fuel gauge still shows charge remaining. The voltage cliff on a new lithium-polymer cell can sit higher than the old cell's mapped cutoff, so the phone cuts out before the percentage reaches zero. Run the recalibration cycle described above first. If shutdowns continue after one full cycle, check that the battery connector is fully seated — a partial connection raises contact resistance and accelerates voltage sag under load, triggering the cutoff at 3.4V or above.