About this replacement
Asus VivoBook S15 S531FA / S531FL — 11.52V Li-Polymer Replacement Battery (B31N1842)
This is an 11.52V, 3550mAh (40.9Wh) Li-Polymer replacement battery for the Asus VivoBook S15 series. It fits the S531FA-EJ003T, S531FA-EJ188T, S531FL-EJ154T, S530FA-EJ269, and over 100 additional VivoBook S15 variants that share the B31N1842 or 0B200-03440000 part number. Voltage, connector pinout, and physical dimensions — 224 × 144 × 6.46mm — match the original cell specification.
- VivoBook S15 S531 and S530 compatibility: These models share the same 3-cell 11.52V architecture, connector, and BMS handshake protocol. The B31N1842 part number spans both the FA and FL sub-variants because Asus used a single battery platform across that chassis generation.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on a VivoBook S15 chassis. The BMS accepted the cell without fault codes, charge current stepped down correctly at the CV phase, and the BIOS read the battery as present and charging from first power-on.
- Post-install calibration on the VivoBook S15: After fitting, run one full discharge until the laptop hibernates on its own, then charge uninterrupted to 100% without using the laptop. This resets the BIOS battery learn cycle 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 cell
The VivoBook S15 BIOS reads health data from the battery's EEPROM, which stores cycle count, rated capacity, and state-of-health flags written by the previous cell. A brand-new cell arrives with its own EEPROM baseline, and the BIOS flags a mismatch until it completes a learn cycle. This is not a fault with the replacement cell. Run one full discharge-to-hibernate followed by an uninterrupted charge to 100% — after that cycle, the BIOS recalculates health against the new cell's actual data and the warning clears.
Laptop shuts down at 20–30% charge shown on screen
This happens when the cell voltage drops below the BMS cutoff threshold under full load — CPU boost plus display backlight together pull more current than the fuel gauge IC accounted for. The percentage shown is based on a calibration curve that hasn't yet been mapped to the new cell, so the displayed figure is ahead of the real state of charge. The fix is two full calibration cycles: discharge to hibernate cutoff, then charge to 100% each time. After two cycles the fuel gauge IC maps the voltage curve accurately and the early shutdowns stop.