We have parked our van away from home for 10 years. Never had to charge the battery! We visit it occasionally, but never run the engine, just check for condensation in winter. If you are worried about the battery, just take van for a spin now and then Just get a good battery, why spend money on a solar panel? Our van is used twice a year to go to France/Spain We do approx 5000 miles a year. Have only change each battery (Engine and domestic) once.