Vehicle-to-grid (V2G) networks are important components of the smart grid (SG) for their capability of providing better ancillary services and facilitating the adoption of renewable resources. The operation of the V2G networks is based on continuously monitoring the status of individual battery vehicle (BV) as well as a carefully designed incentive scheme to attract sufficient participating BVs. However, the close monitoring tends to raise privacy concerns from the BV owners about identity and location information leakage, which have not been considered in previous works. In this paper, we make the first attempt to identify the privacy-preserving issues and propose a precise reward scheme in V2G networks, both of which are important towards bringing the concept of V2G network into practice. In V2G networks, it is the service providers (individual BVs) who need privacy protection rather than the service consumer (power grid). This unique characteristic renders privacy protection solutions proposed for conventional network systems not directly applicable. To protect privacy of BVs in V2G networks, we present , a secure communication architecture which achieves privacy-preserving for both BVs' monitoring and rewarding processes. Extensive performance analysis shows that only incurs moderate communication and computational overheads.