Cooperative relays have been used in many wireless applications to reduce transmit power as well as adding receiver diversity. However, the energy efficiency trade-offs of relay networks have not been thoroughly investigated using a more complete energy model of the system. In this paper we present an energy model for a cooperative dual-relay system using decode-and-forward (DF) protocol with receiver diversity. Energy consumption is based on models of both analog and digital components for transmission and reception. A quartic transmit power amplifier (PA) energy equation is derived that is a function of the following parameters: relay location, relative transmit power allocation amongst the relays, spectral efficiency, transmission distance, pathloss, and target bit-error rate (BER). The energies of the remaining circuit components are added to form a multi-relay DF system energy equation, which is then numerically evaluated to minimize total energy by finding the optimal relay locations, relay transmit PA power allocations, and spectral efficiency. Results are compared to our previous work that considered the energy of direct transmission and a single-relay system, and the minimum-energy system as a function of source-destination distance is considered.