The paper presents the original design of the Off-Grid PV mini-system for powering separate circuits of the residential building. The PV system was used interchangeably for comparative purposes batteries AGM and Li-Ion for energy storage. The PV system provides autonomy to separate building circuits only in the summer months, for Li-Ion energy storage, at the installation location in central Poland. An automatic power switch was used, which turned on the mains supply in the event the battery was discharged. The controller is configured in two ways for priority for solar systems set in summer or priority for the power grid in winter. The next stage of work compares the discharge times of two types of batteries, assuming constant load on the AC side of the inverter. Based on these measurements, the relative autonomy times of the PV system were estimated for the assumed load with different types of batteries in summer and winter. The time of supplying selected circuits of a residential building in the tests conducted for the Li-Ion battery to the AGM battery increased by approx. 50% and increased with increasing load.