IBM ThinkPad i1400 14.4V Replacement Battery 02K6576

IBM ThinkPad i1400 2611 Series — 14.4V Li-ion Replacement Battery (02K6576)

This 14.4V, 4400mAh (63.36Wh) Li-ion battery replaces the original power cell in the IBM ThinkPad i1400 series laptops. It fits multiple 2611 sub-models, including the 552, 40x, 412, and 43x variants (excluding 434 and 435). Voltage and connector match the original IBM specification.

• 2611 series compatibility: These ThinkPad i1400 variants share the same 14.4V battery bay, connector pinout, and BMS handshake protocol — one cell works across all listed sub-models without modification.
• Bench tested on actual hardware: We cycled this cell on a 2611-series ThinkPad, confirmed the BMS handshake completed correctly, and verified the BIOS accepted the cell without triggering an unknown-battery error on first boot.
• Post-install recalibration on ThinkPad i1400: After fitting, run the laptop from full charge down 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 this platform.

Why the ThinkPad i1400 BIOS reports poor battery health after a new cell install

The 2611-series BIOS reads health data from EEPROM stored on the battery's BMS board. When a replacement cell arrives, that EEPROM data reflects the rated chemistry profile, not actual measured capacity from in-system cycles. The BIOS compares its learned baseline against the EEPROM values and flags a mismatch as poor health. Running one full discharge-to-hibernate and an uninterrupted recharge forces the BIOS to rewrite its learned baseline to match the new cell, and the warning clears on next boot.

ThinkPad i1400 shutting down at 20–30% charge shown on screen

This is a voltage cliff failure — the cell voltage drops below the BMS cutoff threshold under combined CPU and display load before the fuel gauge reaches zero. The fuel gauge IC on the original BMS was calibrated to the old cell's discharge curve, so it reads remaining capacity inaccurately until recalibrated. Run two full discharge-to-hibernate cycles followed by full uninterrupted recharges to realign the fuel gauge IC to the new cell's curve. After calibration, the laptop should sustain load down to approximately 10.8V per cell group before the BMS triggers shutdown.