It is not necessary to hire an expert to install an RV battery. Although it is critical to install batteries correctly, following correct instructions is generally not difficult.
The electrical system in an RV is 12 volts, which can be provided by either wiring two 6-volt batteries in series to produce 12 volts or by wiring two 12-volt batteries in parallel to produce a 12-volt supply that provides electricity for longer than a single 12-volt battery.
The battery terminals must be wired in the correct order. Diagrams on sites such as RVBasics.com show how to do this for both series and parallel battery arrangements.