The work tackles energy-aware data gathering problems at clustered robotic networks. A cluster head (CH) robot assigns task with other robots which gathers monitoring data from sensors. After executing their assigned tasks, they send resultant data to it in each cluster. Then, an unmanned aerial vehicle (UAV) with limited battery capacity collects data from CH robots by visiting a portion of them. Under limit of battery capacity of UAV, we aim to collecting data from CH robots with a minimum cost by visiting a subgroup of CH robots among them. UAV make a decision on the CH robots to visit by also caring a set of CH robot in addition to its battery capacity and locations of all CH robots. If exists, a nonvisited CH robot sends data to other CH robots for forwarding data. Data forwarding strategy of each nonvisited CH robot is also considered for this cost optimization. Differently from traditional approaches, we consider fixed battery capacity for UAV. The proposed algorithm is compared for various number of CH robots and priority sets by considering energy consumptions of CH robots, which has an influence on lifetime of the network.