About this replacement
Asus VivoBook V555L / MX555 / 4000 Series — 7.6V Li-Polymer Replacement Battery (C21N1408)
This is a 7.6V, 4700mAh (35.72Wh) Li-Polymer replacement battery for the Asus VivoBook 4000, V555L, MX555, A555LJ, and related models. It replaces OEM part numbers C21N1408, 0B200-01130100, and 0B200-01130300. If your VivoBook no longer holds a charge or powers off unexpectedly, this cell is the direct swap.
- VivoBook V555 / MX555 / 4000 platform fit: These models share the same two-cell Li-Polymer pack format, 7.6V nominal voltage rail, and connector pinout. The BMS handshake protocol is consistent across this generation, so the replacement cell is recognised without any firmware workaround.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on a VivoBook V555L unit. The BMS accepted the new cell without fault codes, and the protection circuit responded correctly to overcharge and over-discharge cutoff thresholds.
- First-cycle calibration after install: After fitting this cell, run a full discharge to the hibernate cutoff point, then charge uninterrupted to 100%. This resets the BIOS battery learn cycle and clears the inaccurate health warning that appears after swapping cells on this platform.
BIOS reporting poor battery health after fitting a new C21N1408 cell
When a new cell goes in, the BIOS still holds EEPROM data from the old pack — cycle count, learned capacity, and health flags. The system compares the new cell's output against stale reference values and flags it as degraded before it has been through a single cycle. This is not a fault with the replacement cell. Run one complete discharge-to-hibernate followed by a full uninterrupted charge, and the BIOS will rewrite those values against the new cell's actual behaviour.
VivoBook shutting down at 20–30% charge shown on screen
The fuel gauge IC calibrates against cell behaviour over several cycles. After a swap, the IC is still working from the old cell's discharge curve, so it misreads the remaining capacity. When the new cell hits a voltage the IC hasn't mapped yet, the system interprets it as empty and cuts power — even though the percentage shown still reads 20–30%. The fix is two to three full discharge-and-charge cycles so the IC relearns the curve. After calibration, shutdowns should stop above 5% and the percentage readout will track accurately. Confirm calibration is complete when the laptop reaches hibernate at a consistent voltage near 6.8V per cell.