Travel trailers
Most travel trailers carry their batteries on the A-frame tongue, in a bracket or plastic battery box, right behind the propane tanks. That spot is easy to reach and gets rain, sun and road spray. Some newer trailers put batteries in a front compartment.
Fifth wheels
Fifth wheels usually keep batteries in a front compartment or on the front frame below the pin box area. Larger fifth wheels may have several batteries on a tray.
Charging from the tow vehicle
The 7-pin trailer plug has a 12-volt charge line from the tow vehicle. It helps a little while driving, but the wire is usually thin, so it charges slowly. For lithium or heavy use, some owners add a DC-to-DC charger.
The breakaway system
Trailers with electric brakes have a breakaway switch that applies the brakes if the trailer separates from the tow vehicle. Many breakaway systems draw from the trailer battery. A dead battery can mean the breakaway can't work. Test it per your trailer's manual.
Florida tips
Battery boxes on the tongue get hot in the sun. Corrosion is common near the coast. Keep terminals clean and coated, and the box lid closed.