About this replacement
Asus VivoBook F542UF — 7.6V Li-Polymer Replacement Battery (C21N1634)
This is a 7.6V, 4900mAh (37.24Wh) Li-Polymer battery for the Asus VivoBook F542UF and related VivoBook variants including the R542UF and R542UQ series. It matches OEM part numbers C21N1634, C21PQCH, 0B200-02550000, and 0B200-02550200. Install it when the original cell no longer holds a usable charge or fails to power the laptop off mains.
- VivoBook F542 and R542 platform fit: These models share the same two-cell Li-Polymer pack format, 7.6V voltage rail, and SMBus BMS handshake. The connector and cell housing are physically identical across the F542UF, R542UF, and R542UQ variants, which is why one part number covers all of them.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a VivoBook F542UF unit. The BMS communicated state-of-charge data correctly over SMBus from the first cycle, and the ASUS battery management driver read capacity and cycle count without errors.
- First-cycle calibration on VivoBook: After fitting this cell, run the laptop on battery until it hibernates at low charge cutoff, then charge uninterrupted to 100%. This one full discharge-to-hibernate cycle 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 VivoBook F542UF shuts down at 20–30% shown after a battery swap
The fuel gauge IC on the F542UF learns discharge curves from the previous cell and stores them in EEPROM. When a new cell is installed, the IC is still referencing the old cell's end-of-life voltage floor, so it miscalculates the remaining capacity. Under full CPU and display load, the new cell hits the IC's stale cutoff threshold before the gauge reaches zero. Running two to three complete discharge-to-hibernate cycles recalibrates the fuel gauge IC against the new cell's actual voltage curve and eliminates the early shutoff.
BIOS reporting battery health as "poor" or "replace battery" immediately after fitting a new cell
This warning is driven by EEPROM data carried over from the old cell, not a fault in the new one. The Asus BIOS reads cycle count and state-of-health flags from the battery's SMBus EEPROM, and a degraded old cell leaves behind unfavourable values that persist after the swap. The fix is straightforward: complete one full discharge-to-hibernate cycle followed by an uninterrupted charge to 100%. After that charge completes, the BIOS battery learn cycle refreshes the stored health data and the warning clears — confirm by checking MyAsus or BIOS Battery Information at 100% charge.