Wireless sensor networks become more and more attractive for a broad variety of application scenarios. Wireless Sensor Network (WSN)s are cheap and can be easily deployed as well as that they require by design low maintenance effort. But running installations are still rare, because real world requirements and environmental conditions are even today a big challenge. Especially in multi-hop networks a minimum lifetime of several years can not be achieved globally. In this paper, we present a Fair Energy Trade Multi-Hop Routing (FET-MHR) protocol for Wireless Sensor Networks guaranteeing a minimum network lifetime. We introduce a routing metric that implements a fair energy trade among all nodes. Nodes with low energy resources and links with a bad quality index are avoided. By that we take into account the energy spent for sending in the past (low battery) as well as energy needed for sending in the future (bad link quality). Considering both aspects when selecting routing paths including their metrics helps increasing the node's lifetime significantly. We evaluated our protocol in simulations and compared it with various existing routing metrics. We demonstrate that our protocol can achieve better lifetimes for sparse and for dense network setups.