About this replacement
Lenovo IdeaPad C340-14IWL — 15.36V Li-Polymer Replacement Battery (L18C4PF3)
This is a 15.36V, 2850mAh (43.78Wh) Li-Polymer battery for the Lenovo IdeaPad C340-14IWL and related 14-inch convertible models. It replaces the original L18C4PF3 cell when the laptop stops holding charge, fails to accept power, or the BIOS flags the battery health as poor. It also fits the IdeaPad C340-14API, IdeaPad Flex-14API, and the 81N6004UGE variant.
- C340 and Flex-14API platform fit: These models share the same 15.36V four-cell Li-Polymer architecture, identical connector pinout, and BMS handshake protocol — so one cell covers all listed variants without any modification.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on an IdeaPad C340-14IWL. The BMS handshake completed on first connect, the charge controller accepted the cell without fault codes, and capacity reporting stabilised after two full cycles.
- Post-install calibration for the C340: After installing, run one full discharge to hibernate-cutoff, then charge uninterrupted to 100%. This resets the BIOS battery learn cycle and clears the inaccurate health warning that appears after every cell swap on this platform.
BIOS reporting battery health as poor after fitting a new cell
The C340 BIOS reads health data stored in the old cell's EEPROM, not the new cell's actual chemistry. When a new cell is installed, that cached data no longer matches, so the system flags poor health immediately. This is not a fault with the replacement — it is a data mismatch. Run the battery learn cycle (full discharge to hibernate, uninterrupted charge to 100%) and the BIOS will re-map health against the new cell's actual behaviour.
Laptop shuts down at 20–30% shown on the gauge
This happens when the fuel gauge IC has not yet calibrated against the new cell's discharge curve. The gauge loses accuracy early, and the laptop interprets the voltage drop as a critical low-battery event before the real capacity is exhausted. The fix is two to three full charge and discharge cycles — each one lets the fuel gauge IC re-map the voltage-to-capacity curve. After calibration, the shutdown threshold should align with the actual 3.0V per-cell cutoff.