About this replacement
IBM ThinkPad 390 Series — 11.1V Li-ion Replacement Battery (02K6610)
This 11.1V, 6600mAh Li-ion battery replaces the original pack in the IBM ThinkPad 390, 390E, 390X, and 1720. It matches OEM part numbers 02K6610, 02K6611, 05K6610, ASM 02K6535, FRU 02K6513, FRU 02K6520, and FRU 11J8923. Capacity is rated at 73.26Wh — consistent with what the original IBM spec sheet called for.
- ThinkPad 390 platform fit: The 390, 390E, 390X, and 1720 all share the same battery bay geometry, 11.1V rail, and connector pinout. The BMS handshake protocol is identical across this generation, so one cell replaces all listed models without adapter or modification.
- Bench tested on actual hardware: We cycled this cell on a ThinkPad 390-series unit and confirmed the BMS initialised correctly, the OS recognised the pack without fault codes, and charge current stepped down normally at the top-of-charge threshold.
- First-use calibration on ThinkPad 390: After installing, 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 this platform.
Why the ThinkPad 390 shuts down at 20–30% shown on the fuel gauge
The ThinkPad 390's fuel gauge IC was calibrated against the original cell's discharge curve. A new cell with fresher chemistry has a slightly different voltage-to-capacity slope. When the CPU and display pull full load, voltage drops faster than the gauge predicts, and the system hits its low-voltage cutoff before the displayed percentage reaches zero. Run two full discharge-to-hibernate and full-recharge cycles to let the fuel gauge IC re-map the new cell. After calibration, shutdown should not occur above 5–8% remaining.
BIOS reporting the replacement pack's Wh rating as incorrect
The BIOS reads Wh data from an EEPROM embedded in the battery pack. The value stored there reflects the rated chemistry spec, which can differ slightly from the measured capacity of new cells. This is an EEPROM data difference — not a fault with the pack. The battery operates correctly regardless of what the BIOS displays. If the reported Wh value matters for your deployment, run a full calibration cycle first — the OS-level power manager on this platform updates its estimate after one complete discharge and recharge.