Busbar welds are crucial in battery pack assembly, as their quality directly affects the structural integrity, electrical conductivity, and thermal efficiency of the battery pack. Aluminum alloys are favored for busbar due to their lower cost and weight. However, aluminum laser welds are prone to porosity, which negatively impacts weld strength and electrical resistance. This study explores the effect of circular laser beam oscillation parameters (frequency and amplitude) on keyhole stability, bubble reabsorption, and weld porosity in battery busbar welding through a combined experimental and computational approach. Lap joints were produced under zero gap condition using circular beam oscillation, with systematic variations in oscillation frequency and amplitude.  The results reveal that the oscillation amplitude plays a dominant tole in enhancing keyhole stability by widening the keyhole and reduction porosity.  Additionally, the distance between the laser beam and the melt pool boundary was found to be crucial in pore formation, as longer distances allow bubbles to stay longer in the melt pool and be reabsorbed by the keyhole.  By examining melt pool geometry and the underlying mechanisms of bubble formation and reabsorption, new insights were gained into the physical processes that prevent keyhole collapse and facilitate bubble reabsorption, leading to a significant reduction in weld porosity. These findings advance laser welding techniques for aluminum alloys in e-mobility applications by providing a pathway to improved weld quality through keyhole dynamics.