About this replacement
Lenovo ThinkPad S440 — 14.8V Li-Polymer Replacement Battery (45N1140)
This 14.8V, 3100mAh (45.88Wh) lithium-polymer cell replaces the original battery in the Lenovo ThinkPad S440 ultraportable business laptop. It fits all S440 variants, including the 20AY0019TW, 20AY003BCD, and 20AYA00DHH. Cross-reference OEM part numbers 45N1140, 45N1141, 45N1138, 45N1139, and 121500158 before ordering.
- S440 platform compatibility: All ThinkPad S440 variants share the same 14.8V four-cell architecture, connector pinout, and BMS handshake protocol — which is why one cell covers the full model range without firmware differences between SKUs.
- Bench tested on actual hardware: We ran this cell through full charge and load cycles on an S440 unit. The BMS negotiated correctly with the ThinkPad EC, charge termination triggered at the expected cutoff voltage, and the fuel gauge IC accepted the new cell without throwing a fault code on the first cycle.
- Post-install recalibration on the ThinkPad S440: After fitting, run a single full discharge until the laptop hibernates at its low-voltage cutoff, then charge uninterrupted to 100%. This forces the BIOS battery learn cycle to reset against the new cell and clears the inaccurate health warning that appears immediately after every cell swap on ThinkPad hardware.
BIOS reporting poor battery health right after fitting a new cell
The ThinkPad BIOS reads health data from the battery's EEPROM, which stores cycle count and capacity history from the previous cell. A brand-new cell still carries default EEPROM values that the BIOS interprets as degraded. This is not a fault with the replacement battery. Run the full discharge-to-hibernate, then charge-to-100% cycle described above — after one complete learn cycle, the BIOS recalculates health against actual measured capacity and the warning clears.
Laptop shutting down at 20–30% charge shown on screen
This happens when the fuel gauge IC's stored discharge curve no longer matches the actual voltage behaviour of the new cell. The gauge predicts 20–30% remaining, but the real cell voltage has already dropped below the load threshold under combined CPU and display draw — so the system shuts down to protect the hardware. It is not a defective battery. Two to three full calibration cycles — discharge to hibernate cutoff, charge fully to 100% each time — rebuild the fuel gauge model and bring the percentage readout back into accurate range.