About this replacement
Asus Zenbook UX31LA — 11.1V Li-Polymer Replacement Battery (C32N1301)
This is an 11.1V, 4500mAh (49.95Wh) Li-Polymer battery for the Asus Zenbook UX31LA ultrabook. It replaces OEM part numbers C32N1301 and 0B200-00510000. Compatible models include the UX31LA-0161A4200U, UX31LA-R5017H, UX31LA-XH51T, and 19 additional UX31LA variants.
- UX31LA platform fit: All UX31LA variants share the same thin-pack form factor, three-cell Li-Polymer configuration, and BMS connector pinout. The 315.50 x 127.52 x 6.65mm dimensions match the chassis cavity exactly, and the BMS handshake protocol is consistent across the full UX31LA production run.
- Bench tested on actual hardware: We ran this cell through full charge and discharge cycles on a UX31LA unit. The BMS negotiated correctly with the Asus EC firmware — charge current ramped, balancing engaged at top of charge, and cutoff triggered cleanly at low voltage without any error flags.
- Post-install calibration on the UX31LA: After fitting, run one full discharge to hibernate cutoff, then charge uninterrupted to 100%. This resets the BIOS battery learn cycle and clears the inaccurate health warning that appears after every cell swap on this platform.
Why the UX31LA BIOS reports poor battery health after a cell swap
The UX31LA stores battery health data in the old cell's EEPROM. When you install a new cell, the BIOS reads a mismatch between the stored wear data and the fresh cell's capacity response — it flags this as degraded health. This is a firmware behaviour, not a fault with the replacement cell. One full discharge-to-hibernate followed by an uninterrupted charge to 100% triggers the BIOS learn cycle and rewrites the health register correctly.
UX31LA 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 gauge estimates remaining charge based on the old cell's profile, so it reads 25% while the actual cell voltage has already dropped below the safe cutoff point. The laptop shuts off abruptly because the voltage cliff arrives before the gauge reaches zero. Run two to three full discharge-and-charge cycles and the fuel gauge IC will recalibrate its endpoints — shutdowns at false percentages stop after that.