Asus VivoBook K401 11.4V Replacement Battery B31N1424

Asus K401 Series — 11.4V Li-ion Replacement Battery (B31N1424)

This is an 11.4V 4200mAh (47.88Wh) Li-ion replacement battery for the Asus VivoBook K401 series, including the K401LB, K401LB5010, and K401LB5200. It replaces OEM part numbers B31N1424 and 0B200-01390000. Fits the compact three-cell configuration used across this ultrabook lineup.

• K401 series compatibility: All models in this lineup share the same 11.4V three-cell architecture, B31N1424 connector pinout, and BMS handshake protocol — the same replacement cell covers the full range without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a K401LB unit. The BMS accepted the new cell cleanly, protection thresholds triggered correctly at both ends, and the charge IC reached termination without fault flags.
• First-cycle calibration on the K401: After fitting, run the laptop on battery until it hibernates from low charge, then charge uninterrupted to 100% without interruption. This resets the BIOS battery learn cycle and clears the inaccurate health warning that appears after every cell swap on this platform.

Why the K401 shuts down at 20–30% after a battery swap

The K401's fuel gauge IC builds a capacity model from the previous cell's discharge curve. A new cell has different internal resistance and a steeper voltage cliff at lower states of charge. The BIOS reads the old curve, sees a voltage drop it doesn't expect, and triggers a protective shutdown before the cell is actually empty. Running two full discharge-to-hibernate and full recharge cycles forces the fuel gauge to rebuild its model against the new cell's actual curve.

BIOS reporting battery health as poor or unknown after fitting a new cell

The K401's BIOS reads health status from EEPROM data written during the original cell's service life — cycle count, capacity fade history, and wear flags are all stored there. A new cell doesn't overwrite that data automatically. The "poor health" flag reflects the old cell's recorded state, not the physical condition of the replacement. Complete one full learn cycle — discharge to hibernate cutoff, then charge to 100% uninterrupted — and the BIOS will rewrite the health register against the new cell's baseline.