12 Volt Switch

I'd suggest to visit Walmart and get a marine/deep cycle battery with number designation "DC-**". The "DC" designation has larger plates inside than the other Walmart offerings. Try to get the largest battery that will fit the case. While you're there shop for a battery master disconnect switch. You want this so you can flip a switch rather than disconnecting a battery terminal every time you put the trailer in storage. Without disconnecting the battery, the trailer's parasitic loads like circuit boards, radio memory. and alarms will suck your new battery dead in a week or two. Do that a few times and your new battery will be your old dead battery.