As far as I know, there is no special battery made just for SUVs or RVs. They use the same batteries made for cars, trucks, boats, etc.
For an SUV or a boat to run lights and such what you need is called a deep cycle battery. This type of battery can be discharged more deeply without damage than a standard auto cranking battery.
If you need a battery for starting the engine
you will do better to use a regular starting battery.
However if you can get these batteries for free then how can you go wrong? Even if it is a starting battery it will work fine for running boat lights and such. Probably won't last as long as a deep cycle battery but for free who cares if you get 4 years instead of 6.