In this paper, the preparation and characteristics of all-solid-state thin film batteries (TFB) are described. In contrast to the state-of-the-art TFB preparation processes, only room temperature processes are used. The cathode is based on amorphous molybdenum(VI) oxide (MoO3), for the electrolyte lithium phosphorus oxynitride (LiPON) is employed and lithium metal acts as anode active material. The cycling stability and rate performance were examined and are discussed. The material set shows a very high cycling stability and excellent rate capability. Performing 550 full cycles at a current density of 202.5 μA cm−2 (10C) a discharge capacity fade of around 15% could be observed. Furthermore, at higher current densities of 2 μA cm−2 (145C) about one third of the initial discharge capacity remained. Using the proposed technology a shift from inorganic rigid substrates, such as glass to flexible polymer substrates is enabled. The performance of the MoO3/LiPON/Li TFBs on glass and flexible polyimide substrates were tested and are discussed within this paper.