<p>Buffer-aided cooperative Non-Orthogonal Multiple Access (NOMA) enhances spectral efficiency by enabling multiple users to simultaneously access the same resources, thereby supporting large-scale connectivity. This capability is particularly valuable in beyond 5&#xa0;G systems, where the demand for massive device connectivity is critical. Wireless-powered communication via energy harvesting has emerged as a promising approach to address the escalating connectivity requirements driven by the rapid growth of connected devices. To fully leverage energy harvesting in buffer-aided cooperative NOMA networks, relay selection mechanisms must account for both the relay’s available energy and its data content to mitigate potential outages. This study applies a relay selection strategy tailored for energy-harvesting buffer-aided cooperative NOMA systems. The selection scheme evaluates the status of both the data buffer and the energy buffer when selecting a relay. The appropriateness of the selection strategy for accumulating energy via both source-to-relay and inter-relay charging (IRC) is examined in this paper. Simulation results reveal that the performance of the proposed selection strategy is notably improved in terms of both network outage probability and throughput when inter-relay charging is taken into account. Furthermore, this performance improvement scales with the number of relays deployed. The findings also highlight how variations in energy and data buffer sizes influence the overall network performance.</p>