About this replacement
Asus Eee Book E403SA — 11.4V Li-Polymer Replacement Battery (C31N1431)
This 11.4V, 4800mAh (54.72Wh) Li-Polymer cell replaces the original C31N1431 battery in the Asus Eee Book E403SA and related models. It fits the Eee PC E403SA, VivoBook E403NA, and Eee Book E403S, among others. The battery uses the same three-cell configuration as the original, maintaining the correct voltage rail for the motherboard's power delivery circuit.
- E403SA/E403NA platform fitment: These models share the same slim chassis, identical connector pinout, and a common BMS handshake protocol tied to the C31N1431 part number. The BIOS reads cell authentication data from the battery's EEPROM — using the correct part number avoids a false "unknown battery" flag in Windows.
- Bench tested on actual hardware: We cycled this cell through full charge and controlled discharge on an E403SA board. The BMS reported correct Wh rating, charge current tapered normally at 100%, and no overcurrent trip occurred during CPU-plus-display stress load.
- Post-install calibration on the E403SA: After fitting this battery, 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.
Why the E403SA BIOS flags a new battery as "poor health" or "unknown"
The E403SA BIOS reads health data cached in the battery's EEPROM and compares it against its own stored baseline from the previous cell. A fresh battery has a different EEPROM state, so the BIOS logs a mismatch and reports degraded health — even at 100% charge. This is not a fault with the replacement cell. Running one full discharge-to-hibernate and a complete uninterrupted recharge forces the BIOS to rewrite its baseline against the new cell's data. After that cycle, the health status updates to normal.
E403SA shutting down at 20–30% charge shown on screen
This happens when the fuel gauge IC's calibration still reflects the old, degraded cell rather than the new one. The IC predicts remaining capacity from voltage curves it learned on a worn battery, so it hits the voltage cliff earlier than the new cell actually warrants. The laptop cuts power because the predicted voltage drops below the shutdown threshold — even though real charge remains. Run two to three full discharge-to-hibernate and full-recharge cycles without interruption; by the third cycle, the fuel gauge recalibrates its curve and the shutdowns stop.