This research aims to investigate and analyze the optimal beta radioisotopes for use in betavoltaic batteries, focusing on enhancing a betavoltaic battery’s performance and efficiency. We conducted a comprehensive analysis of 1252 radioisotopes, among which are 955 beta emitters and 502 beta-minus decay modes. We identified 27 pure beta emitters and further narrowed these down to select the most suitable candidates for betavoltaic applications. We utilized the ICRP 107 report and DECDATA auxiliary software to evaluate some characteristics and features of beta emitters. Our evaluation led to the selection of two groups of radioisotopes—3H and 63Ni from pure beta emitters, and 147Pm, 151Sm, 171Tm, and 155Eu from impure beta emitters—based on their power, minimum volume factor, and cell and source dimensions. The selected radioisotopes demonstrate the potential to significantly improve betavoltaic battery design, offering a balance between energy output and realistic dimensions for practical applications. The findings provide a framework for selecting and utilizing suitable beta emitter radioisotopes, which is crucial for advancing betavoltaic battery technology. Our results contribute to a deeper understanding of the characteristics required for optimal radioisotope selection, paving the way for more efficient and compact betavoltaic batteries.