Recent advancements in wireless charging technology offer promising alternative to address the challenging problem of energy consumption in low-power networks. Based on these breakthroughs, existing solutions have investigated wireless charging strategies of low-power networks through the use of mobile chargers, where a charger has to come at the nodes' vicinity to recharge their battery. However, none of these works have considered the multihop energy transmission, whose feasibility have been demonstrated recently. In such a system, a node can transmit energy wirelessly to its neighbors. In this paper, we propose an optimization model to determine the minimum number of chargers needed to recharge the elements of a network in a multihop scenario, taking into acccount the energy demand of the nodes, the energy loss that occurs during a transfer and the capacity of the chargers. To the best of our knowledge, the work presented in this paper is the first that addresses the optimization of multihop wireless energy transfer in low-power networks.