My new to me and used RV came with two 12V House Batteries and would show 10.8 V just a short time after unplugging from shore power, so I knew I had to replace them. Some off brand car batts. Yep, those gotta go.
Limped along for 3 months with them not able to hold a charge until I finally got up here to Oregon (with no sales tax). Went to Costco here in Portland and got a quote for Interstate golf cart batts (2X 6 Volt) @ $85 each. Not bad. I'd have to install them myself, but they'd cart them out to the RV for me, remove the old batteries, lift them up to the tray, and cart off the old batts. Nice. All I had to do was connect three wires.
{Did check an Interstate battery center here in town and they wanted $154 each! Costco it is! Not a hard decision afterall.}
Hoping that they'll last 7-10 years. They are taller than the brackets the RV manufacturer installed for the OEM batteries so I'm fairly confident they'll do the job for a long time.