About this replacement
Sony Ericsson T610 Series — 3.7V Li-ion Replacement Battery (BST-25)
This is a 3.7V 700mAh Li-ion cell replacing the BST-25 battery in Sony Ericsson T610 series phones. It fits the T610, T606, T608, and T610NZ among others. Swap it in when the original cell no longer holds a charge through a normal day of calls and messaging.
- T610 series fit: The T610, T606, T608, and T610NZ all use the same BST-25 footprint — same 3.7V rail, same three-contact connector, and the same BMS handshake the phone's charge IC expects. One cell covers the whole group.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a T610 unit. The BMS accepted the charge IC handshake without error, voltage held stable under screen and modem load, and the protection circuit tripped correctly at the low-voltage cutoff threshold.
- Fuel gauge recalibration on first use: After installing this cell, run one full discharge down to automatic shutdown, then charge uninterrupted to 100%. The T610's fuel gauge IC was calibrated to the original cell's discharge curve — one complete cycle resets the coulomb counter against the new cell before the readings become trustworthy.
Why the T610 reports wrong battery percentage after a cell swap
The T610 uses a coulomb-counting fuel gauge IC that tracks charge state by measuring current in and out of the cell over time. When the original cell ages, the phone recalibrates its baseline to that degraded curve. A new 700mAh cell has a steeper, healthier discharge curve — the stored baseline no longer matches. Until the IC runs one full cycle on the new cell, the percentage display will read high or drop suddenly. Run one complete discharge to shutdown, then a full charge, and the gauge will track accurately.
Sudden shutdown at 20–30% on the replacement cell
This is a voltage cliff issue, not a capacity problem. During an active call or backlight-on screen event, current draw spikes and the cell voltage drops sharply. If the fuel gauge IC still holds the old degraded cell's internal resistance model, it underestimates how close the new cell is to the protection cutoff. The BMS trips at 3.0V per cell and shuts the phone down before the display percentage reaches zero. One full calibration cycle — discharge to auto-off, charge to 100% — corrects the internal resistance estimate and eliminates the premature cutoff.