About this replacement
Asus UL30Vt Series — 14.8V Li-ion Replacement Battery (A42-UL30)
This 14.8V 6600mAh Li-ion battery replaces the A42-UL30, A42-UL50, and A42-UL80 cells across the Asus UL30, UL30A, UL30Vt, and UL30A-A1 series ultraportable notebooks. It slots into the same bay as the original and connects to the same charging circuit. Rated capacity is 97.68Wh.
- UL30 and UL50 and UL80 platform fitment: These three model lines share the same 14.8V four-cell battery architecture, the same physical connector, and the same BMS handshake protocol — which is why one part number covers all three. The voltage rail and communication pinout are identical across the platform.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a UL30A chassis. The BMS completed its handshake, the charging circuit ramped to 16.8V peak without fault codes, and the fuel gauge IC registered the new cell capacity correctly after two full cycles.
- First-cycle calibration on the UL30Vt: After fitting, run the battery down to hibernate cutoff under normal use — do not force-drain it. Then charge it uninterrupted to 100%. This resets the BIOS battery learn cycle and clears the inaccurate health warning that appears on the first boot after any cell swap.
Why the UL30Vt BIOS reports poor battery health immediately after a cell swap
The BIOS reads health data from the battery's EEPROM, which stores cycle count and rated capacity figures from the previous cell. A new battery carries fresh EEPROM data that does not match the degraded history the BIOS was tracking. The mismatch triggers a "poor health" or "replace battery" warning even though the new cell is fully functional. Running one complete discharge-to-hibernate followed by an uninterrupted full charge allows the BIOS learn cycle to rewrite its internal reference against the new cell's actual voltage curve.
UL30Vt shutting down at 20–30% battery remaining shown on screen
This happens when the fuel gauge IC has not yet calibrated against the new cell's chemistry. The IC is still using voltage-to-capacity mapping data from the old degraded cell, so it misjudges where the real voltage cliff sits. Under combined CPU and display load, actual cell voltage drops faster than the gauge predicts — the BMS protection circuit trips and the laptop shuts down before the displayed percentage reaches zero. Complete two full discharge-to-hibernate and uninterrupted-charge cycles; by the third cycle the fuel gauge IC recalibrates and the shutdown threshold corrects to below 5% remaining.