BST-25 Sony Ericsson T610 Replacement Battery 3.7V 1200mAh

Sony Ericsson T610 / T606 / T608 — 3.7V Li-Polymer Replacement Battery (BST-25)

This is a 3.7V, 1200mAh lithium-polymer replacement for the BST-25 battery used in Sony Ericsson T610, T606, and T608 handsets. It fits the original battery compartment and connects via the stock multi-pin connector. At 4.44Wh, capacity matches the original cell specification.

• T610 / T606 / T608 fit: These models share the same battery bay geometry, connector pinout, and charge IC handshake — one BST-25 cell serves all three. The BMS communicates pack temperature and charge state to the phone's power management IC over the same data line.
• Bench tested on actual hardware: We cycled this cell through the T610's charge IC and confirmed the BMS handshake completes without error. The protection circuit tripped correctly on an overload test and resumed normal operation after load removal.
• Fuel gauge recalibration on first install: After fitting this cell, run one full discharge down to automatic shutdown, then charge uninterrupted to 100% before normal use. The T610's fuel gauge IC maps its percentage readings against the old cell's discharge curve — one complete cycle corrects that calibration against the new cell.

Why the T610 reports wrong battery percentage after a cell swap

The T610 uses a coulomb-counting fuel gauge IC that builds its percentage model from the previous cell's discharge history. A new cell has a different internal resistance and discharge curve, so the IC's stored model no longer maps correctly. The phone may report 40% and shut down moments later, or show 100% well before the charge cycle completes. One full discharge-to-shutdown followed by a complete uninterrupted charge resets the counter and aligns the IC to the new cell's actual curve.

Sudden shutdown at 20–30% on the replacement cell

This happens when the cell voltage drops sharply under the load spikes from the GSM modem or backlight — a behaviour called voltage cliff. The fuel gauge still shows 20–30% because it is tracking charge count, not real-time cell voltage. A fresh lithium-polymer cell with a slightly higher internal impedance than the original will sag below the phone's 3.0V cutoff before the counter reaches zero. After two full calibration cycles the IC learns the new cell's sag characteristics and shutdown point shifts back toward 5–8% where it belongs.