In this article, we propose an energy -aware load monitoring model, called e-Mon, for enabling energy aware load balancing in Peer-to-Peer (P2P) systems. P2P is a scalable and self-organizing technology for utilizing computational resources of the end-user devices for the benefit of a computing system. In P2P systems, the need for fair balance of load is crucial since the end-users need to be incentivized to participate in the system. The short battery life, caused by additional strain on the computational resources of the end-user devices, is a significant negative incentive factor for mobile end-users of current P2P systems. The e-Mon model, proposed in this article, enables moving load from energy-critical to less energy-critical nodes in P2P systems. This is done by including the energy status of a peer node as one of the factors defining a nodes load. The model helps saving the energy of mobile P2P nodes, particularly in cases when the remaining battery capacity is low. The article provides a thorough energy efficiency evaluation demonstrating that e-Mon can significantly improve the battery life of mobile nodes by improving the quality and fairness of load balance between heterogeneous nodes. With a proper selection of a load balancing model for the application scenario, e-Mon is shown to achieve up to 470% battery life extension compared to the case with traditional load balancing with no battery monitoring. (C) 2016 Elsevier Inc. All rights reserved.