Solar energy has become one of the most potential alternative energies in the world. To convert solar energy into electricity, a photovoltaic (PV) system can be utilized. However, the fluctuation of sunlight intensity throughout the day greatly affects the generated energy in the PV system. A battery may be beneficial to store the generated energy for later use. A DC–DC converter is commonly exploited to produce a constant output voltage during the battery charging process. A Zeta converter is a DC–DC converter which can be used to produce output values above or below the input voltage without changing the polarity. To deal with the inherent non-linearity and time-varying properties of the converter, in this paper the sliding mode control (SMC) is first analyzed and exploited before being integrated with a proportional-integral (PI) control to regulate the output voltage of the PV system. Disturbances are given in the form of changes in input voltage, reference voltage, and load. Voltage deviation and recovery time to reach a steady-state condition of the output voltage after disturbances are investigated and compared to the results using a proportional-integral-differential (PID) controller. The results show that the proposed control design performs faster than the compared PID control method.