Marine batteries are recommended for recreational vehicles because of their deep capacity and long service life. Deep cycle marine batteries from brands like DieHard provide a lower CCA rating but have the power you need to continuously run your electronics, making them a good pick for RV use. Gel cell batteries have the same technology as lead-acid marine batteries, but they use gel for an electrolyte rather than liquid. This helps prevent leaks when the battery is off center or on its side due to rough waters or other sailing conditions.
The battery in your car uses a series of cells that consist of lead and lead oxide plates submerged in an electrolyte that's about 65% water and 35% sulfuric acid. It's a bit of an oversimplification, but the size of the plates and the amount of electrolyte have a big effect on how much electricity a lead/acid battery can store.
For the 'chassis battery' that actually starts the engine in your RV, a heavy-duty automotive battery will do the trick - all that's expected of an automotive battery is a big burst of voltage and amperage for a short time. For the 'house battery' that runs 12V accessories on your RV, you need something with a lot of reserve power. That means a conventional lead/acid battery with heavier lead plates that can stand a deep discharge cycle, or possibly an absorbed glass mat (AGM) battery. AGM batteries use a fibrous mat between plates, saturated in 90% electrolyte, for a deeper reserve capacity. Some RVs are also designed for two 12V batteries in parallel, or even four 6V batteries wired in parallel. Regardless of what you use, be sure you go with the right size/CCA rating, keep your batteries maintained and don't let them get too depleted before charging.