RVs typically charge their house battery bank through three paths: shore power (plugging into a campground’s AC outlet through an onboard converter), solar panels, or the vehicle’s alternator while driving — often all three feeding the same battery bank through a charge controller that prevents them from fighting each other.
Practical note
Off-grid and RV charging systems are more forgiving of imperfect setups than people expect — the main failure mode is undersizing the battery bank or solar input relative to actual daily use, not choosing the wrong charger.