Ad-hoc networks can be used to increase the radio range of hotspot scenarios and the number of prospective clients. However, the constraints created by the nature of wireless links and low power devices pose many challenges to this integration. Charging and efficient forwarding are two key functionalities in an ad-hoc network in order to allow its integration in the existing infrastructure networks. This paper proposes a lightweight and secure Session-Aware charging protocol (SACP) for these environments. This protocol is able to provide guarantees of cooperative behavior in traffic forwarding, with minimal network overhead. The performance results, evaluated in multiple environments, show the protocol merits in terms of throughput and network overhead.