In this paper we focus on integration of batteries with ship power systems for three application cases. Presented application cases include two platform supply vessels, one equipped with diesel engines and other with dual fuel engines, and a heavy lift crane vessel. Besides reducing the number of running engines and maintaining original dynamic positioning capabilities, we also demonstrate novel possibilities of battery usage, such as harvesting of waste energy, and implementation of dual fuel engines for dynamic positioning. In all application cases, results indicate significant fuel savings and reduction of running hours due to spinning reserve function of batteries.