About this replacement
Lenovo ThinkBook 14 G4 IAP Series — 11.64V Li-Polymer Replacement Battery (L21C3PD5)
This 11.64V, 3850mAh (44.81Wh) Li-Polymer battery replaces the original cell in the Lenovo ThinkBook 14 G4 IAP series. It fits models including the 21CX0036MJ, 21CX000GUK, 21CX001LMZ, 21CX002NKR, and over 130 additional variants. OEM part numbers L21C3PD5, L21D3PD5, L21L3PD5, and L21M3PD5 all cross to this cell.
- ThinkBook 14 G4 IAP platform fit: All ThinkBook 14 G4 IAP variants share the same 3-cell Li-Polymer architecture, 11.64V rail, and BMS connector pinout. The fuel gauge IC handshake is identical across this generation, so one cell covers the full model range without firmware conflicts.
- Bench tested on actual hardware: We ran this cell on a ThinkBook 14 G4 IAP unit and monitored BMS communication through full charge and discharge cycles. The protection circuit responded correctly to charge cutoff, thermal thresholds, and discharge floor without triggering false fault flags.
- Post-install calibration cycle: After fitting this cell, run the laptop down to hibernate-cutoff on battery alone, then charge uninterrupted to 100% without using the machine. This forces the BIOS battery learn cycle to reset against the new cell's actual capacity and clears the inaccurate health warning that appears after every cell swap.
BIOS reporting poor battery health immediately after replacement
The ThinkBook 14 G4 IAP stores battery state data in EEPROM on the original cell. When you swap in a new cell, the BIOS reads that EEPROM as blank or mismatched and flags the battery as degraded or unknown — even though the cell is new. This is a data state issue, not a hardware fault. Running one full discharge-to-hibernate followed by an uninterrupted charge to 100% completes the BIOS learn cycle and writes fresh capacity data to the new cell's EEPROM. After that cycle, the health reading in Lenovo Vantage or the BIOS battery screen should return to normal.
Laptop shuts down at 20–30% charge shown on the OS gauge
This happens because the fuel gauge IC has not yet calibrated against the new cell's voltage-to-capacity curve. The old curve it stored predicts a safe voltage floor at 30% — but the new cell's actual floor sits lower, so the system cuts power before the gauge catches up. It is not a faulty cell. Run two to three full discharge and charge cycles without interruption, and the gauge IC recalibrates its curve to match the new chemistry. By the third cycle, the shutdown point should drop back to the correct low-battery threshold near 5–10V per cell.