About this replacement
Asus UL30Vt Series — 14.8V Li-ion Replacement Battery (A42-UL30)
This is a 14.8V, 4400mAh (65.12Wh) Li-ion replacement battery for the Asus UL30Vt and its close variants. It fits the UL30, UL30A, and UL30A-A1 among others using the A42-UL30, A42-UL50, or A42-UL80 OEM part numbers. The connector and cell count match the original pack so the BIOS reads the battery correctly on first boot.
- UL30 series compatibility: The UL30, UL50, and UL80 lines share a common four-cell 14.8V battery bay and the same BMS communication protocol. That is why one part number — A42-UL30 — covers all three sub-families. The EEPROM data embedded in this pack matches what the Asus EC firmware expects to see at handshake.
- Bench tested on actual hardware: We ran this pack on a UL30A through a full charge and load cycle. The BMS held charge termination at 16.8V as expected, and the fuel gauge IC reported capacity within normal variance. No false low-battery shutdowns triggered during the test.
- First-cycle reset for UL30Vt: After fitting this battery, discharge the laptop to hibernate cutoff under normal use, then charge uninterrupted to 100% without using the machine. This gives the UL30Vt's battery learn cycle a clean baseline and clears the inaccurate health warning that appears after every cell swap.
Why the UL30Vt BIOS flags a new battery as poor health
The Asus EC firmware reads health data from the pack's EEPROM, not from live cell measurements. A new cell ships with cycle count and wear data zeroed out, which the BIOS interprets as a mismatch against the original battery's stored profile. This produces a "battery not detected" or "poor health" warning on first boot even when the pack is electrically sound. Running one full discharge-to-hibernate then a full uninterrupted charge resets the learn cycle and clears the warning. If it persists after two full cycles, check the BIOS is on the latest firmware version.
UL30Vt shutting down at 20–30% charge shown
This happens when the fuel gauge IC has not yet calibrated against the new cell's actual discharge curve. The gauge was trained on the old, degraded cell, so it miscalculates the voltage cliff point on the replacement. Under full CPU plus display load the new cell's voltage drops faster than the gauge predicts, triggering an emergency shutdown before the displayed percentage reaches zero. Two to three full discharge-and-charge cycles recalibrate the gauge. After the third cycle, the cutoff should stabilise at or below 5% displayed charge, around 14.4V under load.