The main function of a backup power system is to supply an application, such as a fortification or other critical functions, at the event of a power outage. Contemporary backup power systems mainly comprise combustion engines, with optimal efficiency at higher power outputs than those of normal operation. Traditionally, the size of a backup power generator is governed by a load point´s maximum power demand, rather than its average power demand. This implies that the combustion engine, in various degrees, more often runs at lower power outputs, and therefore at suboptimal efficiency. Hybridization, i.e. combining the combustion engine with a battery, allows the engine to operate closer to its optimal power output. This project has experimentally evaluated the performance of a diesel power unit and a commercial battery system, that supplies a load with a maximum power demand of 63 kW, represented in the system as a generic consumption profile. The experiments also supports power quality assessment, which outlines a superior quality from the battery system compared to the diesel power unit. Experimental measurement data could be applied in a project-developed simulation model, to evaluate hybridized solutions in both parallel- and serial mode. The report also presents an overview of commercial battery chemistries, in combination with considerations for operation room design. Peak fuel savings for a 7 h and 38 min case were determined to be 8,8 kg (25 %), or 1,15 kg/h. These savings were accomplished with both a parallel- and serial configuration and a battery system with 99 kWh capacity. Simulations also showed that smaller battery systems correspond to similar fuel savings.