The Smart Grid (SG) aims to transform the current electric grid into a "smarter" network 1 where the integration of renewable energy resources, energy efficiency and fault tolerance are the 2 main benefits. This is done by interconnecting every energy source, storage point or central control 3 point with connected devices, where heterogeneous SG applications and signalling messages will 4 have different requirements in terms of reliability, latency and priority. Hence, data routing and 5 prioritization are the main challenges in such networks. So far, RPL (Routing Protocol for Low-Power 6 and Lossy networks) protocol is widely used on Smart Grids for distributing commands over the 7 grid. RPL assures traffic differentiation at the network layer in wireless sensor networks through 8 the logical subdivision of the network in multiple instances, each one relying on a specific Objective 9 Function. However, RPL is not optimized for Smart Grids, as its main objective functions and their 10 associated metric does not allow Quality of Service differentiation. In order to overcome this, we 11 propose OF QS an objective function with a multi-objective metric that considers the delay and the 12 remaining energy in the battery nodes alongside with the dynamic quality of the communication links. 13 Our function automatically adapts to the number of instances (traffic classes) providing a Quality of 14 Service differentiation based on the different Smart Grid applications requirements. We tested our 15 approach on a real sensor testbed. The experimental results show that our proposal provides a lower 16 packet delivery latency and a higher packet delivery ratio while extending the lifetime of the network 17 compared to solutions in the literature. 18