About this replacement
Asus N591LB / Q551LN Series — 11.4V Li-ion Replacement Battery (B31N1402)
This is an 11.4V, 4000mAh (45.6Wh) Li-ion replacement battery for the Asus VivoBook N591LB and Q551LN series laptops. It replaces OEM part numbers B31N1402, 0B200-01050000M, and 0B200-01050000. Fit models include the N591LB, Q551LN, Q551, and Q551LN-BBI706.
- N591LB and Q551LN platform fit: Both models share the same three-cell battery bay, connector pinout, and BMS handshake protocol under the B31N1402 part number. The 11.4V nominal rail matches the motherboard's power regulation circuit for both variants.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the Q551LN platform. The BMS communicated correctly with the BIOS, capacity reporting stabilised after two full calibration cycles, and the protection circuit triggered at the correct low-voltage cutoff.
- BIOS learn cycle after install: After fitting this battery, run one full discharge down to hibernate cutoff, 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 this platform.
Why the N591LB shuts down at 20–30% remaining after a battery swap
The BIOS stores discharge curve data from the original cell in firmware memory. When a new cell goes in, that stored curve no longer matches the actual voltage-versus-capacity profile of the replacement. The system reads a voltage drop under CPU and display load and interprets it as a near-empty cell, triggering a hard shutdown. Running two full discharge-to-hibernate and uninterrupted full-charge cycles re-trains the fuel gauge IC against the new cell's actual curve and eliminates the premature cutoff.
BIOS reporting 0% or "unknown battery" immediately after fitting
This is an EEPROM mismatch, not a dead cell. The BIOS reads battery identity data from the cell's EEPROM and compares it against cached values from the previous battery. A fresh cell returns different serial and cycle-count data, which the BIOS flags as unrecognised. Boot into the BIOS setup utility, navigate to the power or battery section, and clear stored battery data if that option is present — otherwise, a cold boot with the battery connected and AC power removed forces the BIOS to re-initialise communication with the new cell. Charge to 100% and recheck the status report.