About this replacement
Asus X455LA Series — 7.6V Li-Polymer Replacement Battery (C21N1409)
This is a 7.6V, 5000mAh (38Wh) Li-Polymer battery for the Asus VivoBook X455LA laptop. It replaces the original cell when the existing pack no longer holds adequate charge for portable use. Compatible models include the X455LA, X455LA-WX078H, X455LA-WX063D, X455LA-WX080D, and over 400 additional X455 variants.
- X455 series compatibility: All covered models share the same 7.6V two-cell Li-Polymer architecture, the same board connector pinout, and the same BMS handshake protocol — which is why one part number covers the full X455LA lineup without modification.
- Bench tested on actual hardware: We cycled this cell on an X455LA board and confirmed the BMS negotiated charge termination correctly at 8.72V, held current through full discharge without tripping undervoltage protection prematurely, and reported state-of-charge accurately to the EC after two calibration cycles.
- First-cycle calibration on the X455LA: After installation, run the laptop on battery until Windows triggers hibernate-cutoff, then charge uninterrupted to 100% without interruption. This resets the embedded controller's battery learn cycle and clears the low-health warning the BIOS flags after every cell swap.
Why the X455LA BIOS flags a new battery as poor health immediately after swap
The X455LA's embedded controller reads EEPROM data from the old cell and caches it as the baseline for health scoring. When a new cell arrives with different EEPROM charge history, the EC compares it against the cached values and flags a mismatch as degraded health — even though the physical cell is new. This is not a fault with the replacement battery. Running one full discharge-to-hibernate cycle followed by an uninterrupted charge to 100% forces the EC to rewrite its baseline against the new cell's data, and the warning clears on next boot.
X455LA shutting down abruptly at 20–30% charge shown
This happens when the cell voltage drops below the EC's cutoff threshold under combined CPU and display load, even though the fuel gauge IC still shows 20–30% remaining. The fuel gauge calibration is wrong — it was mapped to the old cell's discharge curve, not the new one. The fix is the same learn cycle: discharge fully to hibernate-cutoff, then charge uninterrupted to 100%. After two full cycles the fuel gauge IC recalibrates its curve to the new cell and the premature shutdown stops. Confirm the cell voltage at rest reads between 7.4V and 8.4V before starting the calibration.