About this replacement
IBM ThinkPad T61 7659 / T400 2764 — 10.8V Li-ion Replacement Battery (ASM 42T5265)
This is a 10.8V, 4400mAh (47.52Wh) Li-ion battery for the IBM ThinkPad T61 and T400 series laptops. It fits the ThinkPad T61 7659, T61 6480, T400 2764, R400, and over 60 additional ThinkPad variants sharing the same battery slot and connector. Voltage and connector match the OEM spec — no modifications needed.
- ThinkPad T61 and T400 platform fit: These models share a common battery bay, connector pinout, and BMS handshake protocol across the 42T4xxx and 42T5xxx OEM part families. One cell works across the full range because Lenovo kept the voltage rail and SMBus communication spec consistent throughout this ThinkPad generation.
- Bench tested on actual hardware: We ran this cell on a ThinkPad T400 and monitored SMBus data through the charge cycle. The BMS communicated correctly with the EC, charge current tapered normally at full capacity, and the cell reported accurate state-of-charge data back to the firmware throughout.
- BIOS learn cycle after install: After fitting this battery, run the laptop down to hibernate cutoff on battery alone, then charge uninterrupted to 100% without using the machine. This resets the BIOS battery learn cycle and clears the inaccurate health warning that appears after every cell swap — the warning is normal and goes away after one full calibration pass.
Why the ThinkPad T61 reports a replacement battery as "poor health" in Power Manager
ThinkPad Power Manager reads battery health from EEPROM data embedded in the battery's BMS chip. A new cell ships with factory EEPROM values that don't match the charge history the laptop expects to see, so the software flags it as degraded. This is a firmware comparison mismatch, not a cell fault. One full discharge-to-hibernate followed by an uninterrupted charge to 100% writes a new baseline to the BIOS and clears the warning. After two or three full cycles, Power Manager will report health accurately.
ThinkPad shutting down at 20–30% battery remaining shown on screen
The fuel gauge IC estimates remaining charge based on voltage curves calibrated to the original cell's chemistry profile. When a new cell is installed, that profile is mismatched until the IC runs calibration cycles against the actual cell. Under full CPU and display load, the real cell voltage drops below the cutoff threshold before the displayed percentage reaches zero — the laptop shuts down to protect the cell. To fix this, run two full discharge-to-hibernate and full-recharge cycles without interrupting the charge. After calibration, the shutdown threshold and the displayed percentage will align to within a few percent at 10.8V nominal.