About this replacement
Asus AsusPro PU401 Series — 11.1V Li-Polymer Replacement Battery (C31N1303)
This is an 11.1V, 3950mAh (43.85Wh) Li-Polymer replacement battery for the Asus AsusPro PU401 series ultrabook. It fits the PU401LA, AsusPro Essential PU401LA, and PU401LA-XB51, among others. The OEM part numbers it replaces are C31N1303 and 0B200-00470000.
- PU401 series fit: These models share the same three-cell Li-Polymer battery bay, connector pinout, and BMS handshake protocol. The battery slots into the same physical footprint at 292.50 × 72.34 × 11.18mm with no modification needed.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a PU401LA. The BMS communicated correctly with the BIOS, reported accurate state-of-charge, and the protection circuit triggered at the expected low-voltage cutoff threshold.
- First-cycle recalibration on the PU401: After installing, run one full discharge until the laptop hibernates, then charge uninterrupted to 100%. This forces the BIOS battery learn cycle to reset against the new cell and clears the inaccurate health warning that appears after every cell swap on this platform.
Why the PU401 BIOS flags a new battery as poor health
The PU401 stores battery health data in EEPROM on the old cell. When you swap the cell, the BIOS reads no matching EEPROM record and defaults to a poor health or unknown status flag. This is a data mismatch, not a fault with the replacement cell. Running a full discharge-to-hibernate followed by an uninterrupted charge to 100% initiates the learn cycle and writes fresh calibration data to the new cell's EEPROM. After one or two full cycles, the health status normalises.
Laptop shuts down at 20–30% charge shown on the PU401
This happens when the fuel gauge IC is still calibrated to the old cell's discharge curve. The displayed percentage no longer matches actual cell voltage, so the laptop cuts off before the gauge reaches 0%. It is not a fault in the replacement cell — it is a calibration lag. Run two or three full discharge-to-hibernate and full-charge cycles without interruption. By the third cycle the fuel gauge IC re-maps to the new cell's curve and the readings stabilise to within a few percent of actual remaining capacity.