About this replacement
Lenovo ThinkBook Plus 20TG Series — 15.36V Li-Polymer Replacement Battery (L18C4PF0)
This is a 15.36V, 2850mAh (43.78Wh) Li-Polymer battery for the Lenovo ThinkBook Plus 20TG006XAU and related ThinkBook 13s and 14s models. It replaces OEM part numbers L18C4PF0, L18D4PF0, and L18M4PF0, along with several 5B10 and SB10W series part numbers. Use this when the original cell no longer holds charge or fails to register in the BIOS.
- ThinkBook 13s, 14s, and Plus 20TG compatibility: These models share the same 15.36V four-cell Li-Polymer architecture, connector pinout, and BMS handshake protocol — which is why a single part number covers the full range without firmware conflicts.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a ThinkBook unit. The BMS negotiated correctly with the EC, charge current ramped as expected, and the cell reached full capacity without triggering an over-voltage cutoff.
- Post-install discharge cycle for ThinkBook units: After fitting this battery, run the laptop on battery power until Windows forces hibernate, 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 ThinkBook firmware.
BIOS reporting poor battery health immediately after replacement
The ThinkBook BIOS reads health data stored in the old cell's EEPROM and caches it. When a new cell is installed, the BIOS has not yet run a learn cycle against the new chemistry, so it flags the battery as degraded or unknown. This is not a fault with the replacement cell — it is a firmware calibration issue. Run one full discharge-to-hibernate then an uninterrupted charge to 100% to force the EC to rewrite the health register. After two to three full cycles, the BIOS health indicator should read normal.
Laptop shuts down at 20–30% charge shown on new battery
This happens when the fuel gauge IC has not yet calibrated against the new cell's actual voltage curve. The IC is still referencing the old cell's discharge profile, so it miscalculates the remaining capacity and signals a low-voltage shutdown too early. The cell voltage at that point is typically still above 14.0V — the shutdown is a false reading, not a real cutoff. Run three full discharge and charge cycles without interruption, and the fuel gauge IC will recalibrate its internal model to match the new cell.