About this replacement
IBM ThinkPad R60 / T60 Series — 10.8V Li-ion Replacement Battery (40Y6799)
This is a 10.8V, 8800mAh (95.04Wh) Li-ion replacement battery for the IBM ThinkPad R60, R61, and T60 series laptops. It cross-references over 30 OEM part numbers including FRU 92P1137, ASM 92P1138, 42T4504, and 43R9252. The original battery in these mid-2000s business notebooks degrades over charge cycles, and this cell restores portable operation.
- ThinkPad R60, R61, and T60 compatibility: These three chassis share the same 10.8V battery rail, connector pinout, and BMS communication protocol. IBM used a common battery bay across this generation, so one cell covers all three platforms without modification.
- Bench tested on actual hardware: We ran this cell in a ThinkPad T60 and confirmed the BMS handshake completed on first boot. The BIOS recognised the battery, reported charge state correctly, and the protection circuit responded normally to a full discharge cycle.
- Post-install calibration on ThinkPad R60 / T60: After fitting this cell, run a full discharge to hibernate cutoff, then charge uninterrupted to 100% without removing AC power. This resets the ThinkPad BIOS battery learn cycle and clears the inaccurate health warning that appears after a cell swap on this platform.
BIOS reporting battery health as poor after fitting a new cell
The ThinkPad BIOS stores capacity and cycle data in an EEPROM register linked to the original cell. When a new battery is installed, the BIOS compares current readings against stale EEPROM data and flags a health mismatch. This is not a fault with the replacement cell — it is a data mismatch between the new chemistry and the old register values. Running one full discharge-to-hibernate followed by an uninterrupted charge to 100% forces the BIOS to rewrite the learn cycle data against the new cell's actual capacity.
Laptop shutting down at 20–30% charge shown on screen
This happens when the cell voltage drops below the BMS cutoff threshold under combined CPU and display load, even though the fuel gauge still reads 20–30%. The fuel gauge IC is calibrated against the old cell's discharge curve, so it misreads remaining capacity until it completes a full calibration cycle against the new cell. The voltage cliff is real — the cell hits cutoff voltage before the gauge catches up. Run two to three full discharge and charge cycles and the fuel gauge IC will recalibrate its curve to match the new cell, pushing the reported shutoff point below 5%.