IBM ThinkPad Z60t Replacement Battery 10.8V 40Y6791

IBM ThinkPad Z60t — 10.8V Li-ion Replacement Battery (40Y6791)

This is a 10.8V, 4400mAh Li-ion battery for the IBM ThinkPad Z60t notebook series, including the Z60t 2511, 2512, and 2513 variants. It slots into the standard battery bay and connects via the ThinkPad multi-pin dock connector. OEM part numbers covered include 40Y6791, ASM 92P1122, FRU 92P1121, and FRU 92P1123.

• Z60t series compatibility: All Z60t variants listed share the same 10.8V three-cell-pair architecture, identical bay dimensions, and the same six-pin battery connector with BMS handshake lines — so one cell works across the whole sub-family without modification.
• Bench tested on actual hardware: We ran this cell through a full charge-discharge cycle on a Z60t 2512 and confirmed the BMS communicated correctly with the BIOS — charge acceptance reached 100% and no fault codes were thrown during the session.
• First-cycle calibration on the Z60t: After fitting, run the laptop on battery until Windows forces hibernation, then plug in and charge uninterrupted to 100%. This forces the ThinkPad BIOS to complete its battery learn cycle and clears the inaccurate health warning that appears after every cell swap.

BIOS reporting poor battery health immediately after fitting a new cell

The ThinkPad BIOS stores learned capacity data in EEPROM and compares it against the new cell on first contact. Because the old cell's wear data is still cached, the BIOS flags the replacement as degraded before it has run a single cycle. This is a firmware state issue, not a fault with the cell. One complete discharge-to-hibernate followed by a full uninterrupted charge clears the cached data and lets the BIOS write fresh capacity values. After that cycle, the health indicator should return to normal.

ThinkPad Z60t shutting down at 20–30% charge shown on screen

The fuel gauge IC on the Z60t estimates remaining charge based on a voltage curve calibrated to the previous cell's chemistry and age. A new cell has a steeper voltage cliff at the lower end of the discharge curve, so the IC underestimates how close to cutoff the battery actually is and the system shuts down before the gauge hits zero. This is not a defective cell — it is a calibration mismatch. Run two to three full discharge-to-hibernate, then full charge cycles and the fuel gauge IC will re-map its curve against the new cell; the early shutdowns will stop. Target a resting voltage of 10.8V at 100% state of charge to confirm the cell is performing correctly.