About this replacement
Asus B31N1902 — 11.52V Li-Polymer Replacement Battery
This is an 11.52V, 3550mAh (40.9Wh) lithium-polymer battery built to replace the OEM B31N1902 cell in compatible Asus notebooks. It fits models that shipped with this part number from the factory. If your original battery no longer holds charge or your laptop drops off AC unexpectedly, this cell swaps in directly.
- B31N1902 platform fitment: Asus uses the B31N1902 across a specific notebook line sharing the same 11.52V three-cell architecture, connector pinout, and BMS handshake protocol. Swapping a cell from a different voltage group — even a physically similar one — will cause the BMS to reject the pack or refuse charging entirely.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on B31N1902-compatible hardware. The BMS accepted the pack without fault codes, charge termination triggered correctly at capacity, and voltage held stable under combined CPU and display load without triggering a protection cutoff.
- Post-install calibration step: After fitting this cell, run the laptop down to hibernate-cutoff on battery only, then charge uninterrupted to 100%. This resets the BIOS battery learn cycle and clears the inaccurate health warning that appears after every cell swap on Asus notebooks.
BIOS reporting poor battery health immediately after fitting the new cell
When you replace the B31N1902, the BIOS still holds EEPROM data from the old, degraded cell. It compares the new cell's reported state against that stored history and flags a health warning — not because the new cell is faulty, but because the learn cycle hasn't run yet. One full discharge-to-hibernate followed by an uninterrupted charge to 100% clears this. After two or three full cycles, the BIOS recalibrates and the warning disappears.
Laptop shuts down at 20–30% charge shown on screen
This is a voltage cliff, not a calibration issue. Under combined CPU and display load, the cell voltage drops faster than the fuel gauge IC can track — the system hits the low-voltage protection threshold before the displayed percentage reaches zero. The fix is calibration: fully discharge to hibernate-cutoff under normal use load, then charge to 100% without interruption. After two full calibration cycles, the fuel gauge IC maps the new cell's actual discharge curve and the early shutdowns stop.