About this replacement
Asus X555 Series — 7.6V Li-Polymer Replacement Battery (C21N1347)
This is a 7.6V, 4800mAh (36.48Wh) lithium-polymer cell that replaces the original C21N1347 battery in the Asus X555 laptop series. It fits the X555, X555LA, X555LD, X555LN, and over 296 additional X555 variants. Install it when the original cell no longer holds charge or the system shuts down unexpectedly on battery power.
- X555 series fit: Every X555 variant in this line shares the same 7.6V two-cell Li-Polymer architecture, the same connector pinout, and the same BMS handshake protocol. That is why one part number covers the full range from X555LA through to X555LN and beyond.
- Bench tested on actual hardware: We ran this cell on an X555LA and cycled it through charge and discharge under full CPU and display load. The BMS reported correct voltage at each state-of-charge threshold and did not trip on load transitions.
- First-cycle calibration on X555: After fitting, run the laptop on battery until it hibernates on its own, then charge uninterrupted to 100% without using the machine. This gives the fuel gauge IC a full-range sweep against the new cell and resets the learn cycle the BIOS uses to calculate remaining capacity.
BIOS reporting poor battery health immediately after fitting a new cell
The Asus BIOS reads health data cached from the old battery's EEPROM and flags the new cell as degraded before it has completed a single cycle. This is not a fault with the replacement — it is stale data from the previous cell persisting in firmware. 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 charge curve and the warning clears.
Laptop shuts off at 20–30% charge shown on the X555
This happens when the cell voltage drops below the BMS cutoff threshold before the fuel gauge reaches zero — a calibration gap, not a defective cell. The fuel gauge IC built into the X555 board maps percentage to voltage curves learned from the previous battery. On a fresh cell those curves do not match yet. Complete two full discharge-to-hibernate and full-charge cycles back-to-back. After the second cycle the gauge recalibrates and the shutdown point shifts back toward 0%.