About this replacement
Lenovo ThinkPad T440 / X240 Series — 11.1V Li-ion Replacement Battery (45N1134)
This is an 11.1V, 4400mAh (48.84Wh) Li-ion cell for the Lenovo ThinkPad T440, T440S, X240, X240S, and over 160 additional ThinkPad models sharing the same battery bay and connector. It replaces OEM part numbers 45N1134, 45N1737, 45N1135, and the full 45N11xx family. Install it when the original cell no longer holds charge or the system refuses to leave AC power.
- T440 and X240 platform compatibility: These models share a common 11.1V three-cell architecture, the same bottom-bay latch connector, and an identical BMS handshake protocol. That shared electrical spec is why one cell covers both the T440 and X240 chassis lines without firmware conflict.
- Bench tested on actual hardware: We ran this cell on a T440 and X240S unit. The BMS initialised cleanly, charge current stepped correctly through CC and CV phases, and the protection circuit tripped at the expected over-discharge threshold without requiring a manual reset.
- BIOS learn cycle after install: After fitting this cell, run the laptop down to hibernate cutoff on battery alone, then charge uninterrupted to 100%. This forces the ThinkPad BIOS to complete its battery learn cycle against the new cell and clears the false "poor health" warning that appears after every cell swap.
BIOS reporting battery health as poor immediately after replacement
The ThinkPad BIOS stores learned capacity data from the previous cell in its battery EEPROM. When a new cell goes in, the BIOS compares current readings against that stale data and flags a health warning — even when the replacement cell is fully functional. This is not a fault with the cell itself. Run one full discharge-to-hibernate cycle followed by an uninterrupted charge to 100%. The BIOS resets its learned parameters against the new chemistry after that cycle completes.
Laptop shutting down at 20–30% remaining on the gauge
This happens when the fuel gauge IC still holds calibration data from the degraded original cell. The displayed percentage is calculated against old capacity baselines, so the gauge reads 25% while the actual cell voltage has already hit the BMS cutoff threshold. The cell is not faulty — the gauge IC needs two or three full discharge and charge cycles to recalibrate against the new cell's actual voltage curve. After those cycles, the cutoff should align with readings below 5%. If the shutdown persists past three cycles, check that the cell voltage at shutdown reads above 9V with a meter on the battery terminals.