About this replacement
Asus ExpertBook B9450FA — 7.7V Li-Polymer Replacement Battery (C21N1903)
This 7.7V 4155mAh (31.99Wh) Li-Polymer cell replaces the original C21N1903 battery in the Asus ExpertBook B9450FA and its variants, including the BM0165R and BM0280R configurations. The B9450FA is an ultrabook built around portability, so battery health directly affects how long it stays off the charger. Voltage and connector match the OEM spec — no adapter or modification needed.
- B9450FA platform compatibility: The B9450FA, B9450F, and their variant suffixes all share the same 7.7V two-cell Li-Polymer pack format with identical connector pinout and BMS handshake protocol. That is why one part number — C21N1903 — covers the full range.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on a B9450FA unit, confirmed the BMS accepted the handshake without fault codes, and verified the fuel gauge IC began reporting charge state correctly after two full calibration cycles.
- First-cycle reset after install: After fitting this cell, run the laptop down to hibernate cutoff on a normal workload, then charge it uninterrupted to 100%. This gives the BIOS battery learn cycle a clean baseline and clears the inaccurate health warning that appears after any cell swap.
Why the B9450FA BIOS flags a new cell as poor health immediately after replacement
The BIOS reads stored EEPROM data from the previous pack to assess health. When a new cell goes in, that EEPROM data is gone, so the system has no learned charge curve to reference and defaults to a degraded-health flag. This is not a fault with the replacement cell. Running one full discharge-to-hibernate followed by an uninterrupted charge to 100% gives the BIOS enough data to rebuild its learn cycle and clear the warning. After two to three cycles, the reported health figure stabilises.
Laptop shuts down at 20–30% shown on the charge indicator
This symptom appears when the fuel gauge IC is still calibrated against the old cell's discharge curve. Under combined CPU and display load, actual cell voltage drops faster than the gauge predicts, hitting the BMS low-voltage cutoff before the displayed percentage reaches zero. The fix is calibration — discharge fully to hibernate, then charge to 100% without interruption, twice. After two complete cycles, the fuel gauge IC maps the new cell's actual voltage curve and the premature shutdowns stop.