BST-14 Sony Ericsson T68 Replacement Battery 3.7V 750mAh

Sony Ericsson T68 / T68i / C1002S — 3.7V Li-ion Replacement Battery (BST-14)

This is a 3.7V, 750mAh Li-ion replacement for the BST-14 battery used in the Sony Ericsson T68, T68i, and C1002S. These early-2000s candybar phones share the same battery bay and connector, so one cell covers all three models. Capacity matches the original OEM specification.

• T68, T68i, and C1002S compatibility: All three models use the same 3.7V rail, identical physical connector, and the same BMS handshake protocol. One BST-14 cell fits all without modification or adapter.
• Bench tested on actual hardware: We cycled this cell on a T68i unit. The BMS accepted charge on first connection, current limiting engaged correctly at top-of-charge, and the protection circuit tripped as expected under a deliberate short-load test.
• Fuel gauge recalibration on first use: After fitting this cell, run one complete discharge down to automatic shutdown, then charge uninterrupted to 100% before normal use. The T68's fuel gauge IC was calibrated to your old degraded cell — one full cycle resets the reference curve and prevents erratic percentage readings from the start.

Why the T68 reports wrong battery percentage after a cell swap

The T68 uses a simple coulomb-counting fuel gauge IC that stores a discharge curve based on your old cell's behaviour. When you install a fresh 750mAh cell, the IC is still referencing the degraded curve from the original battery. This causes the phone to report inflated or erratic percentages — typically jumping from 60% to 20% without warning. One full discharge-to-shutdown cycle followed by a complete charge forces the IC to rebuild its reference map against the new cell's actual voltage profile. After that single calibration cycle, percentage reporting stabilises.

Sudden shutdown at 20–30% on the replacement cell

This is a voltage cliff issue, not a capacity problem. Under load — screen backlight, active call, or GSM transmission burst — the cell voltage drops sharply if the fuel gauge IC hasn't yet mapped the new cell's discharge curve. The phone's under-voltage protection trips before the displayed percentage reaches zero. It looks like a dead battery but the cell still holds charge. Perform a full uninterrupted discharge-charge cycle first. If the shutdown persists after calibration, check that resting cell voltage measures at least 3.6V before installation.