About this replacement
Acer Aspire 1640LC / 1691 Series — 14.8V Li-ion Replacement Battery (BT.T5005.002)
This is a 14.8V, 4400mAh (65.12Wh) Li-ion battery for Acer Aspire notebooks. It fits the Aspire 1640LC, 1691, 3002NWLCi, 5001WLCi, and hundreds of related Aspire models. Cross-references include BT.T5005.002, LC.BTP03.003, SQU-401, SQU-525, and BTP-AS1681 among others.
- Aspire 1640 / 1691 platform fit: These Aspire models share a common 14.8V four-cell battery rail and identical connector pinout. The BMS handshake runs at the same SMBus address across the range, so one cell pack covers the full compatibility list without firmware conflicts.
- Bench tested on actual hardware: We ran this cell on an Aspire 1691 chassis. The BMS initialised on first connect, charge current ramped normally through CC phase, and the cell reached 16.8V before the charger stepped down to CV taper. No overcurrent trip or false fault flags observed.
- Post-swap calibration — Aspire BIOS learn cycle: After fitting this cell, run one full discharge to hibernate cutoff, then charge uninterrupted to 100%. This resets the BIOS battery learn cycle and clears the inaccurate health warning that appears after every cell swap on Aspire notebooks.
BIOS reporting battery health as poor immediately after replacement
The Aspire BIOS reads health data from EEPROM registers stored in the old cell's fuel gauge IC. When a new cell arrives, those registers are blank or pre-loaded with factory defaults that do not match the BIOS's expected signature. The system flags this as degraded or unknown health. Run one full discharge-to-hibernate cycle followed by an uninterrupted charge to 100% — this forces the BIOS to rewrite its learned capacity baseline against the new cell's actual chemistry.
Laptop shuts down at 20–30% charge shown on screen
This is a voltage cliff issue, not a calibration glitch. Under full CPU and display load, cell voltage sags faster than the fuel gauge IC can track — the pack hits the low-voltage cutoff threshold while the OS still shows charge remaining. It appears most on Aspire models that have never had a calibration cycle run on the new cell. Discharge fully to hibernate, charge to 100% without interruption, then check whether the OS fuel gauge tracks correctly above 3.2V per cell under load.