About this replacement
Sony Ericsson T200 / T202 — 3.7V Li-ion Replacement Battery (BST-24)
This is a 3.7V, 700mAh Li-ion cell built to the BST-24 specification for the Sony Ericsson T200 and T202 mobile phones. It slots directly into the rear battery bay and connects via the original three-pin contact strip. Capacity figures come from product data — 2.59Wh total energy.
- T200 and T202 platform fit: Both handsets share the same BST-24 footprint, contact pinout, and 3.7V nominal voltage rail. The battery communicates charge state through the centre data pin — the same circuit on both models.
- Bench tested on actual hardware: We ran the cell through a full charge cycle on a T200 and monitored the BMS cutoff at 4.2V charge termination and 3.0V low-voltage cutoff. The protection circuit tripped correctly at both thresholds with no anomalous heat at the contact pins.
- Fuel gauge recalibration on first use: After fitting this cell, run one complete discharge down to the automatic power-off point before recharging fully. The T200's fuel gauge IC was calibrated to the original cell's discharge curve — a single full cycle resets the coulomb counter reference and stops the percentage from jumping.
Why the T200 reports wrong battery percentage after a cell swap
The T200 tracks charge state using a coulomb counter that was calibrated against the original BST-24 cell's specific internal resistance and discharge curve. A new cell has different impedance characteristics, so the counter's reference points no longer match actual voltage. The phone then maps voltage to percentage incorrectly — often reading 100% immediately after partial charge, or dropping suddenly near 20%. One full discharge-to-cutoff and recharge cycle forces the IC to relearn the new cell's curve and realign the displayed percentage.
Sudden shutdown at 20–30% on a replacement BST-24
This happens when the cell voltage drops sharply under the load of an active call or backlight — a voltage cliff the T200's fuel gauge did not predict. A fresh Li-ion cell with uncalibrated impedance data causes the phone to underestimate how close it is to the BMS cutoff threshold of 3.0V per cell. The protection circuit then trips the moment voltage sags under load, even though the displayed percentage still shows charge remaining. Charge to 4.2V, discharge fully to automatic shutdown, and repeat once — this gives the coulomb counter accurate data to predict the voltage sag correctly.