About this replacement
Asus VivoBook S14 S433FA Series — 11.55V Li-Polymer Replacement Battery (C31N1905)
This 11.55V, 4250mAh (49.09Wh) lithium-polymer cell replaces part number C31N1905 in the Asus VivoBook S14 and S15 range. It fits the S433FA-EB095T, S433FA-EB173T, S433FL-EB107T, S533FL-BQ051T, and over 150 additional VivoBook variants sharing the same voltage rail and connector pinout. Install it when the original cell no longer holds charge or the laptop won't run unplugged.
- VivoBook S14/S15 platform fit: All listed S433 and S533 models share the same 11.55V three-cell Li-Polymer architecture, identical 285.90 × 85.00 × 4.60mm footprint, and matching BMS handshake via the 0B200-03580200 connector assembly. One cell works across the entire bracket.
- Bench tested on actual hardware: We cycled this cell on an S433FA unit and confirmed the BMS completed its charge handshake, held steady at 11.55V nominal under display-plus-CPU load, and triggered the low-voltage cutoff cleanly without tripping a false over-discharge fault.
- Post-install recalibration on VivoBook firmware: After fitting, run the laptop down to hibernate cutoff — do not force shutdown — then charge uninterrupted to 100%. This resets the BIOS battery learn cycle and clears the inaccurate health warning the firmware throws after every cell swap.
BIOS reporting poor battery health immediately after replacement
The VivoBook BIOS reads health data stored in the old cell's EEPROM, not from the new cell's actual charge state. When a fresh cell is installed, that EEPROM data is absent or mismatched, so the firmware flags the battery as degraded or unknown. This is not a fault with the replacement cell. Run one complete discharge-to-hibernate cycle followed by an uninterrupted full charge — after two to three cycles, the BIOS recalibrates against the new cell and clears the warning.
Laptop shuts down at 20–30% charge shown on screen
This happens because the fuel gauge IC is still referencing capacity curves from the old, degraded cell. When the new cell hits its actual low-voltage threshold under combined CPU and display load, the firmware has already miscalculated how much charge remains. The result is a sudden shutdown well above the reported zero-percent mark. Discharge the laptop fully to hibernate, charge to 100% without interruption, and repeat twice — the fuel gauge IC recalibrates its curve and the reported percentage will align with actual cell voltage, typically settling at 3.85V per cell at the 50% mark.