About this replacement
Lenovo ThinkBook 16 G4 IAP/ARA Series — 15.36V Li-Polymer Replacement Battery (L21C4PD8)
This is a 15.36V, 4450mAh (68.35Wh) Li-Polymer battery for the Lenovo ThinkBook 16 G4 IAP and ARA series laptops. It replaces OEM part numbers L21C4PD8, L21D4PD8, L21L4PD8, L21M4PD8, and SB11F09739. Confirmed fit across multiple regional SKUs including 21CY001UPB, 21CY002XAD, and 21D10020KR, among 136 additional variants.
- ThinkBook 16 G4 platform fit: The IAP and ARA variants share the same battery bay dimensions, 15.36V four-cell architecture, and BMS communication protocol. One cell covers the full G4 generation regardless of regional SKU suffix.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on ThinkBook 16 G4 hardware. The BMS handshake completed without error, charge current stepped down correctly at the high-SOC taper threshold, and no fault flags were triggered during load cycling across CPU and display draw.
- Post-swap learn cycle for ThinkBook BIOS: After installing this cell, run one full discharge to hibernate cutoff, then charge uninterrupted to 100% without use. This resets the BIOS battery learn cycle and clears the inaccurate health warning that appears after every cell swap on ThinkBook hardware.
Laptop shutting down at 20–30% shown after battery swap
This happens because the fuel gauge IC is still calibrated to the old cell's discharge curve. The new cell hits a voltage cliff under combined CPU and display load before the reported percentage reaches zero. The BIOS interprets the sudden voltage drop as a critical low and forces shutdown. Run two full discharge-to-hibernate cycles followed by uninterrupted charges to 100% — the fuel gauge recalibrates against the new cell's actual curve and the early shutdown stops.
BIOS reporting wrong Wh rating in system information after install
The Wh value shown in Lenovo Vantage or the BIOS power screen is read from EEPROM data stored on the battery controller, not measured from the cells directly. A new cell ships with EEPROM values that may differ slightly from what the old pack reported, so the system info screen can show an unexpected Wh figure. This is a data field difference between packs — it does not affect charge behaviour or capacity. Confirm the cell is charging and discharging normally; the EEPROM-reported figure is not a fault indicator.