Asus BU400A Replacement Battery 7.4V 6750mAh Li-Polymer
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Asus BU400A Replacement Battery 7.4V 6750mAh Li-Polymer - 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
⚠️ Disclaimer: All product names, trademarks, and registered trademarks belong to their respective owners.
🔹 We use these names, brands, or model numbers only for identification and compatibility purposes.
Asus BU400A Replacement Battery 7.4V 6750mAh Li-Polymer - is backordered and will ship as soon as it is back in stock.
Voltage
7.4V
Amp
6750mAh
Asus BU400A / Pro BU400 Series — 7.4V Li-Polymer Replacement Battery (C22-B400A)
This is a 7.4V, 6750mAh (49.95Wh) lithium-polymer replacement battery for the Asus BU400A, BU400V, Pro BU400, and Pro BU400A ultrabook series. It replaces OEM part numbers C22-B400A, 0B200-00160000, and C22-BU400A. Fit these models as a direct swap when the original cell no longer holds a charge or fails to register correctly with the system.
- BU400 and Pro BU400 platform compatibility: The BU400A and BU400V share the same battery bay geometry, connector pinout, and BMS handshake protocol. One cell covers both lines without adapter or modification.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on a BU400A unit. The BMS negotiated correctly, charge termination triggered at the expected voltage ceiling, and protection cutoff engaged at the low-voltage threshold without fault codes.
- First-cycle reset on the BU400A: After installation, 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 almost always appears after a cell swap on this platform.
Why the BU400A BIOS reports poor battery health after a cell swap
The BU400A stores battery health data in EEPROM on the original cell. When you fit a new cell, the BIOS reads that EEPROM baseline and flags a mismatch against the new chemistry profile. This is not a fault with the replacement — it is the firmware reacting to unfamiliar cycle count and capacity data. Running the full learn cycle described above writes fresh calibration data and clears the warning. After two or three full cycles, the BIOS health indicator stabilises.
Laptop shuts down with 20–30% charge still showing on screen
This happens when the fuel gauge IC has not yet calibrated against the new cell's actual discharge curve. The old curve predicts voltage drop incorrectly, so the system hits the low-voltage protection threshold well before the displayed percentage reaches zero. The fix is the same learn cycle: discharge fully to hibernate-cutoff, then charge to 100% without interruption. After two full calibration cycles, the gauge tracks accurately and the early 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
The BU400A BIOS shows the new battery as "unknown" or 0% right after fitting — is the cell faulty?
No. The BIOS is reading EEPROM data from the old cell's baseline and has not yet built a profile for the new one. Discharge fully to hibernate-cutoff, then charge uninterrupted to 100%. This triggers the BIOS learn cycle, writes a fresh profile, and clears the unknown or 0% reading within one to two full cycles.
System info on the BU400A is showing the wrong Wh rating — it lists a lower number than the 49.95Wh spec on the replacement cell.
The Wh figure displayed in Windows or the BIOS is pulled from EEPROM data embedded in the cell, which reflects the OEM-rated capacity under specific test conditions rather than a live measurement. A small variance from 49.95Wh in the system readout is normal and does not indicate a fault. Confirm the cell is charging and discharging correctly — if it cycles without unexpected shutdowns, the battery is functioning within spec.
Charging stops at 80% and never reaches 100% on the BU400A — does this replacement support full charge?
This is almost always a BIOS-controlled charge limit, not a fault with the cell. Asus firmware on several BU400-series units ships with a battery health charging mode active, which caps charge at 80% to reduce long-term cell stress. Open MyASUS or the ASUS Battery Health Charging utility, set the charge limit to full capacity (100%), and the cell will charge to its rated ceiling.
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