About this replacement
Asus ZenBook 14X OLED UX5401EA Series — 11.61V Li-Polymer Replacement Battery (C31N2021)
This 11.61V, 5400mAh (62.69Wh) lithium-polymer battery replaces the original cell in the Asus ZenBook 14X OLED UX5401EA-KN511TS and a wide range of ZenBook 14X and ZenBook 14 Flip OLED models. It matches OEM part numbers C31N2021 and 0B200-04030000. The cell fits the 14-inch OLED ultrabook chassis and connects through the original three-cell series configuration.
- ZenBook 14X and 14 Flip OLED platform fit: The UX5401EA and UN5401QA share the same 11.61V three-cell architecture, connector pinout, and BMS handshake protocol — which is why a single cell covers both the clamshell and the 360-degree flip variants without modification.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on ZenBook 14X hardware. The BMS negotiated correctly with the EC firmware, current draw during OLED-on CPU stress registered within spec, and the protection circuit responded to both overcharge and over-discharge cutoff thresholds as expected.
- Post-swap battery learn cycle on ZenBook BIOS: After installing, run the laptop down to hibernate cutoff on battery only — no AC — then charge uninterrupted to 100%. This forces the embedded controller to relearn the new cell's capacity curve and clears the inaccurate health warning that appears in MyASUS after every cell replacement.
Why BIOS reports poor battery health immediately after fitting a new cell
The ZenBook's embedded controller reads health data from the battery's EEPROM — a small memory chip that stores cycle count, rated Wh, and state-of-health flags written by the original cell during manufacture. When a replacement cell arrives, those EEPROM values don't match what the EC recorded for the old pack, so it flags the battery as degraded before a single charge cycle has run. Running the full discharge-to-hibernate then uninterrupted charge sequence rewrites the learned capacity data and clears the false warning. Until that cycle completes, the health percentage shown in BIOS and MyASUS is not a reliable indicator of the new cell's condition.
ZenBook shutting down at 20–30% charge shown on screen
This happens when the cell voltage collapses under combined CPU and OLED panel load before the fuel gauge IC expects it to — the display is showing a percentage derived from the old cell's discharge curve, not the new one. The voltage cliff hits earlier than the gauge predicts, and the EC shuts the system down to protect the cell. It is not a fault with the replacement battery. Two to three full calibration cycles — full discharge to hibernate, full charge to 100% each time — allow the fuel gauge IC to map the new cell's actual voltage-to-capacity curve and bring the shutdown point back in line with the displayed percentage.