Yup, you need Marine/Deep Cycle (M/DC) batteries. These are different from the starting batteries you see in the engine compartment of a vehicle. The M/DC battery is designed to withstand a steady drain over a somewhat prolonged period before being recharged. A starting battery is designed for a short burst engine starting drain (generally very high current) and then it is immediately recharged by the car's alternator. But, neither battery wants to be deeply discharged. If you can keep the discharge level above 70%, it prolongs battery life.
In my opinion, there's no reason to get an expensive battery design such as AGM or Gel Sealed. A simple flooded lead acid battery will give you the best bang for your bucks. I always got Kirkland batteries from Costco before my recent switch to LiFePO4 batteries and was happy with them.
I'm also happy with my LiFePO4 setup, but it requires charging circuits that are designed for Lithium batteries, and that means a considerable up-front cost. My trailer's new converter is designed for Lithium batteries, as is my new solar controller, a house powered charger and a DC-DC converter that prevents excessive Amperage pull from my tow vehicle when traveling.
- Jack