About this replacement
Asus ZenBook 14 UX433FN Series — 11.55V Li-Polymer Replacement Battery (C31N1811)
This is a 11.55V, 4250mAh (49.09Wh) Li-Polymer battery for the Asus ZenBook 14 UX433 series. It replaces OEM part numbers C31N1811 and 0B200-03080000. Confirmed fit includes the UX433FN-BP8201T, UX433FN-A5080T, UX433FA-A5187R, UX433FA-A5188R, and over 114 additional UX433 variants.
- UX433 platform compatibility: Every UX433 variant in this series shares the same three-cell Li-Polymer configuration, 11.55V voltage rail, and C31N1811 BMS handshake. The connector pinout and physical footprint are consistent across the entire UX433FA and UX433FN production run, so one cell fits the full range.
- Bench tested on actual hardware: We ran this cell on a UX433FN and confirmed the BMS negotiated charge current correctly, cell voltage held stable across light and heavy CPU loads, and the BIOS recognised the battery without error on first boot.
- Post-install calibration on the UX433: After fitting, run the laptop on battery until it shuts down at the low-voltage cutoff, then charge uninterrupted to 100% without using the machine. 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.
BIOS reporting poor battery health immediately after fitting a new C31N1811 cell
The ZenBook's BIOS stores battery health data in EEPROM tied to the original cell's cycle count and capacity history. When a new cell is fitted, that stored data does not reset automatically — the BIOS reads the old figures and flags the new battery as degraded. This is not a fault with the replacement cell. Running one complete discharge-to-cutoff followed by a full uninterrupted charge clears the learned values and forces the BIOS to record a fresh baseline against the new cell's actual capacity.
Laptop shuts down at 20–30% charge shown on the UX433 fuel gauge
This happens when the fuel gauge IC's stored discharge curve no longer matches the new cell's chemistry. The IC predicts shutdown voltage based on old cell data and triggers a cutoff while the display still shows charge remaining. It is not a fault with the cell itself. Run two to three full discharge-to-hibernate cycles followed by full charges — the fuel gauge IC recalibrates its curve against the new cell and the percentage readings stabilise. After calibration, voltage at shutdown should read no lower than 10.0V under load.