Since enrgy is a vlaubale resource in Wireless Sensor Networks (WSNs), it is important to continuously monitor the status of this valuable network resource after network deployment. The information about energy status can be used to early notify both sensors and deployers of resource depletion in some parts of the network. It can also be used to perform energy-efficient routing in WSNs. In this paper, we propose a scheme for monitoring residual energy distributions at different parts of the network through a mechanism called Energy Centric scale (ECscale). ECscale is then used to perform optimal as well as approximate Energy-Centric Routing (ECR) in WSNs with the objective of maximizing the network lifetime. The proposed algorithms make use of a fixed virtual wireless backbone that is built on top of the physical topology. Simulation results show that our scheme is scalable and can provide many folds of energy savings when compared to conventional routing schemes.