The standard battery size in most of the campers is what they call a Group 24 battery. The type is a "Deep Cycle" 12 volt lead acid flooded battery. The group size will sort out the amp ratings as each brand can vary a little. Try to get a true Deep Cycle battery if you can. But it may end up being a RV/Marine deep cycle which is a little different but will work OK. Do not get a car "starter" battery. While they start cars well they do not do well on camper that have long current draws.
Walmart does sell these. They have the standard deep cycle group 24 and they have the Maxx deep cycle group 24. The Maxx has a 2 year warranty the standard a 1 year warranty. These are made by Johnson Controls.
Here is the standard 24DC https://www.walmart.com/ip/EverStart...24DC/180350522
Here is the Maxx 24DC https://www.walmart.com/ip/EverStart...24DC/139801236
Deka use to make the lead acid deep cycle but I cannot seem to find it. All I can find is their AGM battery which is an excellent battery but may be more than you need or want to pay for.
Check the dimensions of your battery box and the angle irons on camper before you get one. Not all battery brand are exactly the same size. Point being, just make sure it fits in your battery case even if it is a 1/8" or so different then your current one.
If you want to upgrade to longer lasting power in the battery, then this gets a little more involved as how much do you want/need? They do make bigger batteries but then the size grows too and you may have to make larger battery holder.
Hope this helps
Current Sunlines: 2004 T310SR, 2004 T1950, 2004 T2475, 2007 T2499, 2004 T317SR
Prior Sunlines: 2004 T2499 - Fern Blue
2005 Ford F350 Lariat, 6.8L V10 W/ 4.10 rear axle, CC, Short Bed, SRW. Reese HP trunnion bar hitch W/ HP DC
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