About this replacement
Asus ZenBook 13 UX331UN / UX331FA Series — 11.55V Li-Polymer Replacement Battery (C31N1724)
This is a 11.55V, 4150mAh (47.93Wh) Li-Polymer battery for the Asus ZenBook 13 UX331UN-EG011T and related UX331 ultrabooks. It replaces OEM part numbers C31N1724 and 0B200-02760400. Fit covers the UX331UN, UX331FA, UX331FAL, and U3100FAL lines.
- UX331 platform compatibility: The UX331 series runs a shared 3-cell Li-Polymer pack across multiple sub-models. All variants use the same 11.55V voltage rail, identical connector pinout, and the same BMS handshake protocol — which is why one cell covers both the UN and FA chassis revisions.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the UX331 platform. The BMS accepted the pack without fault codes, charge termination triggered correctly at full capacity, and thermal cutoff engaged as expected during stress testing.
- Post-install calibration on ZenBook firmware: After fitting this cell, run one full discharge until the laptop hibernates on low battery, then charge uninterrupted to 100%. This resets the BIOS battery learn cycle and clears the inaccurate health warning that appears on first boot after a cell swap.
Why the ZenBook 13 shuts down at 20–30% after a battery swap
The UX331 BIOS stores a discharge curve mapped to the original cell's chemistry profile. When a new cell is fitted, that stored curve no longer matches actual cell voltage under load. At around 20–30% shown, the new cell's voltage under full CPU and display load drops below the BIOS cutoff threshold — even though charge remains. Running two to three full discharge-to-hibernate and full-recharge cycles lets the fuel gauge IC re-map its curve against the new cell and eliminates the early shutdown.
BIOS reporting battery health as "poor" or "replace" immediately after fitting
The health status on the UX331 reads from EEPROM data written by the old cell — not from any live measurement of the new pack. On first boot, the BIOS sees cycle count and wear data from the previous cell's EEPROM and flags it as degraded. This is not a fault with the replacement cell. Run the full discharge-and-recharge calibration cycle, and on most UX331 units the health status clears within two cycles. If MyASUS still shows a warning after three calibration cycles, check that BIOS is updated to the latest version for your sub-model.