About this replacement
Lenovo ThinkBook 16 G6 IRL-21KH006HUA — 7.72V Li-Polymer Replacement Battery (L21D4PG4)
This is a 7.72V, 6350mAh (49.02Wh) Li-Polymer battery for the Lenovo ThinkBook 16 G6 IRL-21KH006HUA laptop. It replaces OEM part numbers L21D4PG4, L21M4PG4, and L20C4PG4. The ThinkBook 16 G6 IRL series uses this cell to power the display, CPU, and onboard hardware during portable use.
- ThinkBook 16 G6 IRL compatibility: These three OEM part numbers — L21D4PG4, L21M4PG4, and L20C4PG4 — share the same 7.72V rail, connector pinout, and BMS handshake protocol on the IRL platform. All three are direct functional equivalents in this chassis.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on ThinkBook 16 G6 hardware. The BMS accepted the cell without fault codes, and the charge controller stepped through its full charge profile without interruption.
- Post-install calibration on ThinkBook 16 G6: After installation, run the battery down to hibernate-cutoff, then charge uninterrupted to 100%. This forces the BIOS battery learn cycle to re-baseline against the new cell and clears the inaccurate health warning that appears after every cell swap.
BIOS reporting poor battery health immediately after replacement
The ThinkBook 16 G6 BIOS reads health data stored in the old cell's EEPROM and carries that data forward when a new cell is installed. Until the learn cycle completes, the BIOS has no fresh baseline to compare against — so it flags the new cell as degraded. This is not a fault with the replacement cell. Run one full discharge to hibernate, then a full uninterrupted charge to 100%. After two to three cycles, the BIOS recalculates health against actual cell behaviour and the warning clears.
Laptop shutting down at 20–30% charge shown on screen
This happens when the fuel gauge IC has not yet calibrated against the new cell's actual voltage curve. The IC is still using the old cell's curve, so it misreads the remaining capacity and triggers a shutdown before the cell is actually empty. The fix is the same learn cycle: discharge fully to hibernate-cutoff, then charge to 100% without interruption. After two full calibration cycles, the reported percentage and the actual cutoff voltage align — target is a shutdown no higher than 3% remaining.