We propose a relay-assisted RF harvesting sensor network (R2FSN) model, where the field nodes having finite battery capacity are powered by RF energy transfer (RFET) from a single relay, thus leading to perpetual sensor network operation. The relay node also forwards the field data to the information sink in a two-hop, half-duplex decode-and-forward fashion. We derive closed-form expression of the average end-to-end signal-to-noise ratio (SNR) for each source-destination link in cooperative R2FSN. The performance improvement provided by R2FSN over conventional RF-powered networks is numerically investigated along with the impact of RFET time and relay location on the maximum and minimum average end-to-end SNR over all links.