About this replacement
Asus W1 Series — 14.8V Li-ion Replacement Battery (A42-W1)
The A42-W1 is a 14.8V, 4400mAh (65.12Wh) Li-ion battery for the Asus W1 notebook line. It fits the W1, W1G, W1Ga, and W1Gc, along with additional W1-series variants. When the original cell no longer holds a charge, this unit restores portable operation without hardware modification.
- W1-series cell compatibility: All W1-series notebooks share the same 14.8V four-cell architecture and connector pinout. The BMS on each model expects the same voltage rail and communication protocol, so one cell swap covers the full W1 range without adapter or firmware workaround.
- Bench tested on actual hardware: We ran this cell through full charge and discharge cycles on W1-series hardware. The BMS handshake completed correctly, charge acceptance reached rated capacity, and no false over-temperature cutoffs triggered during load testing.
- First-cycle recalibration on the W1: After installation, run the notebook down to hibernate cutoff on battery alone, then charge uninterrupted to 100% before use. This forces the W1's fuel gauge IC to learn the new cell's actual capacity curve and clears the inaccurate health warning the BIOS flags after every cell swap.
Why the W1 BIOS flags poor battery health immediately after a cell swap
The Asus W1 stores historical charge data in EEPROM on the battery's protection circuit. When a new cell arrives, that EEPROM either holds default values or data mismatched to the old unit. The BIOS reads this data at POST and flags the battery as degraded before a single charge cycle has run. One full discharge-to-hibernate followed by an uninterrupted charge to 100% rewrites the learn cycle data and clears the warning. After two to three full cycles, the BIOS health reading stabilises.
W1 shutting down at 20–30% charge remaining
This happens when the fuel gauge IC has not yet calibrated against the new cell's voltage curve. The IC is still using the old cell's discharge profile, so it misreads the voltage cliff and signals a low-battery shutdown early. It is not a cell fault. Run two or three full discharge-and-charge cycles without interruption to let the IC map the new curve accurately. After calibration, the gauge tracks remaining charge correctly and the early shutdowns stop. Confirm the cell voltage reads above 14.0V at the point the shutdown previously triggered.