About this replacement
Lenovo Yoga C940-14IIL — 7.7V Li-Polymer Replacement Battery (L18C4PH0)
This 7.7V, 7650mAh (58.91Wh) Li-Polymer cell replaces the original battery in the Lenovo Yoga C940-14IIL 2-in-1 convertible notebook. It fits the full Yoga C940-14IIL range, including the 81Q9 series and regional variants. OEM part numbers L18M4PH0, 5B10T11585, 5B10T11586, and related cross-references all apply to this same cell configuration.
- Yoga C940-14IIL platform fit: Every C940-14IIL variant in the 81Q9 series shares the same battery bay dimensions, connector pinout, and BMS handshake protocol. The voltage rail at 7.7V matches the board's charging IC expectation — swapping in a 7.4V or 7.6V cell will trigger a charge fault on most units.
- Bench tested on actual hardware: We ran this cell on a C940-14IIL unit under combined CPU and display load. The BMS held the charge cutoff correctly at 8.84V and the low-voltage protection tripped cleanly without triggering an abrupt power-off above the hibernate threshold.
- Post-install calibration cycle: After fitting this cell, run one full discharge to hibernate cutoff, then charge uninterrupted to 100% without using the laptop. This resets the BIOS battery learn cycle and clears the inaccurate health warning that appears after every cell swap.
BIOS reporting battery health as poor immediately after replacement
The C940-14IIL BIOS reads battery health data from the cell's EEPROM, not from live voltage measurements. When a new cell arrives, that EEPROM either contains factory default values or data the BIOS doesn't recognise as matching the original cycle history. The system flags it as degraded or unknown before a single charge cycle runs. One full discharge-to-hibernate followed by a complete uninterrupted charge resets this — the BIOS rewrites its battery learn table against the new cell and the health warning clears.
Laptop shuts down at 20–30% shown on the fuel gauge
This is a voltage cliff issue, not a capacity fault. Under full CPU plus display load, the cell's output voltage drops faster than the fuel gauge IC can track — the board sees the voltage fall below its cutoff threshold before the displayed percentage reaches zero. It happens most often during video export, gaming, or sustained bright-screen use. To confirm, watch the battery voltage in Lenovo Vantage or HWiNFO during load — if it dips below 6.0V under stress, the fuel gauge IC needs calibration cycles against the new cell. Run two to three full discharge-charge cycles to let the IC map the new cell's actual discharge curve.