B21N1818 Asus VivoBook 15 X512DA Compatible Battery 7.6V 4050mAh
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B21N1818 Asus VivoBook 15 X512DA Compatible Battery 7.6V 4050mAh - is backordered and will ship as soon as it is back in stock.
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Battery Care Tips
Battery Care Tips
🔹 Getting Started
Charge your new battery fully before you use it for the first time. Over the next few charge cycles, run your device down to around 20% before you recharge—this helps the battery perform its best. After that, charge whenever you need to.
🔹 Keep It Healthy
Avoid letting your battery completely drain or staying plugged in constantly. Both extremes wear it out faster. Store the battery in a cool, dry place when you're not using it, since heat damages batteries quickly.
Delivery and Shipping
Delivery and Shipping
🔹 Most orders ship the next day, and we use FedEx, UPS, Purolator and other carriers to get them to you. Lithium batteries have to ship by ground only, not air or USPS. Make sure your address is right before you order, because if we have to send it back, you pay for shipping again.
Disclaimer
Disclaimer
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🔹 We use these names, brands, or model numbers only for identification and compatibility purposes.
B21N1818 Asus VivoBook 15 X512DA Compatible Battery 7.6V 4050mAh - is backordered and will ship as soon as it is back in stock.
Voltage
7.6V
Amp
4050mAh
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.
Compatible Models
Replaces Part Numbers
Technical Specifications
Product Highlights
- Brand: Asus
- Manufacturer: CS
- Series: Standard
- Color: Black
- Product Type: Li-Polymer
- Battery Type: Li-Polymer
- Warranty: 12 Months
- Bulk Orders: sales@batteryweb.com
Frequently Asked Questions
MyASUS says my new battery is at 0% health — is the replacement cell faulty?
It is not faulty. The VivoBook BIOS reads health data from the cell's EEPROM, and a new cell ships with factory-default values that look wrong to the BIOS. Run one full discharge to hibernate cutoff under normal load — screen on, Wi-Fi active — then charge uninterrupted to 100%. That single learn cycle rewrites the BIOS calibration data and the health warning clears.
Windows is showing a completely wrong Wh rating for the new battery — it says 38Wh but the cell is rated 30.78Wh. What is happening?
The Wh figure Windows displays is pulled from the EEPROM data embedded in the cell, and the rated design capacity stored there can differ from the actual chemistry of the replacement cell. This is a reporting difference, not a functional fault — the cell charges and discharges correctly at 7.6V regardless of what Windows reports. After one or two full calibration cycles the fuel gauge IC updates its running total and the displayed Wh figure will track closer to the real 30.78Wh spec.
The new battery charges fine but the percentage jumps erratically — goes from 45% to 22% in minutes with no heavy use.
The fuel gauge IC on the VivoBook motherboard has not yet built an accurate voltage-to-capacity map for the new cell. It is estimating charge state from a curve calibrated to the old, degraded cell, so percentage readings are unreliable for the first few cycles. Discharge fully to hibernate cutoff twice, charging to 100% each time without interruption. By the third cycle the IC has enough data to track the new cell accurately and the jumping stops.
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