I would get a marine/rv deep cycle battery. I bought the biggest one Wal-Mart had...it was around 100 bucks. Deep cycle will allow you to run the battery very low and recharge without major consequence. I can say that fans use a ton of power from a battery. I run the exhaust fan in our LQ when it's too nice for a/c and if the battery charger is not plugged in or it's not hooked to the truck charging, it will die within about 2 hours of constant running. 

If you plan to use it while you're traveling down the road, you will want to be certain that there is a 12v constant running from the truck plug to the battery.

Also, I bought a little battery charger from Harbor Freight that makes up for small draws, charges, and plugs into our 110v electric so when we camp I can run battery operated things (lights, fans, etc.) without worrying the battery will die. Not the optimum situation, but it works well. Leave it to charge when we go ride, use the lights at night when we get back.