About this replacement
Asus VivoBook 15 X512DA / 17 F712FA Series — 7.6V Li-Polymer Replacement Battery (B21N1818)
This is a 7.6V, 4050mAh (30.78Wh) Li-Polymer replacement battery for the Asus VivoBook 15 and VivoBook 17 notebook range. It fits the X512DA, X512UA, X712FA, F712FA, and over 160 additional VivoBook models sharing the B21N1818 cell platform. Voltage and capacity match the original specification exactly.
- VivoBook B21N1818 platform compatibility: All models in this cluster run a shared 7.6V two-cell Li-Polymer architecture with the same physical connector, BMS handshake protocol, and EEPROM charge table. That is why a single cell part number covers both the 15-inch X512 and 17-inch X712 chassis lines.
- Bench tested on actual hardware: We cycled this cell on a VivoBook 15 X512 chassis, confirmed the BMS accepted the EEPROM handshake on first connect, and verified charge current ramped correctly from the initial low-current phase through to termination at 8.4V.
- First-install calibration for VivoBook BIOS: After fitting this cell, run the laptop down to hibernate cutoff under normal use — display on, Wi-Fi active — then charge uninterrupted to 100%. This resets the BIOS battery learn cycle and clears the inaccurate health warning that appears in MyASUS after every cell swap.
BIOS reporting battery health as poor immediately after replacement
The VivoBook BIOS reads health data from the battery's EEPROM — the new cell carries factory-default values that do not match the charge history the BIOS expects. This mismatch triggers a "poor health" or "replace battery" flag in MyASUS even when the cell is brand new. The fix is a full learn cycle: discharge to hibernate cutoff, then charge to 100% without interruption. After one or two complete cycles, the BIOS recalibrates against the new cell's actual charge curve and the warning clears.
Laptop shutting down at 20–30% charge shown on screen
This happens when the fuel gauge IC has not yet mapped the new cell's voltage-to-capacity curve. An aged or freshly swapped cell can hit a voltage cliff — where cell voltage drops sharply under CPU and display load — well before the percentage shown on screen reaches zero. The OS fuel gauge still thinks there is charge remaining because it is working from stale calibration data. Run two full discharge-to-hibernate and uninterrupted charge-to-100% cycles; the fuel gauge IC recalibrates against the new cell and the premature shutdowns stop.