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Photo‐assisted ion batteries utilize light to boost capacity but face cycling instability due to complex charge/ion transfer under illumination. This study identified photo‐induced proton transfer (photo‐induced PT) as a significant process in photo‐(dis)charging of widely‐used V2O5‐based zinc‐ion batteries, contributing to enhanced capacity under illumination but jeopardizing photo‐stability. Photo‐induced PT occurs at 100 ps after photo‐excitation, inducing rapid proton extraction into V2O5 photoelectrode. This process creates a proton‐deficient microenvironment on surface, leading to repetitive cathode dissolution and anode corrosion in each cycle. Enabling the intercalated protons from photo‐induced PT to be reversibly employed in charge‐discharge processes via the anode‐alloying strategy achieves high photo‐stability for the battery. Consequently, a ~54 % capacity enhancement was achieved in a V2O5‐based zinc‐ion battery under illumination, with ~90 % capacity retention after 4000 cycles. This extends the photo‐stability record by 10 times. This study offers promising advancements in energy storage by addressing instability issues in photo‐assisted ion batteries. [ABSTRACT FROM AUTHOR]