Wearable devices traditionally rely on batteries as the primary source of energy for operation. Batteries are often rigid, bulky, heavy, and require constant recharging, consequently hampering the development of novel device applications. This paper describes a new vision for Body Sensor Networks (BSNs); an interconnection of tiny, flexible, battery-free, cooperative, and programmable wearables via the concept of Intra-Body Power Transfer and Communication (IBPTC), which uses the human body as a medium to exchange energy and data. These wearable devices can receive energy from central, on-body power sources, and coordinate to support whole-system operation and programmer-defined sensing tasks. Of course, this vision entails significant challenges; notably in developing robust hardware and software for energy and information exchange across the body channel, enabling power failure resiliency and timely coordinated task execution. In this paper, we describe a roadmap of systems and tools towards the ultimate vision of battery-free BSNs that has the potential to transform current architectures and designs of BSNs, enabling innovative applications that would otherwise be impossible with on-device batteries.