Upgrade to a made in the USA Trojan battery. We’re authorized dealers and they’re the best you can get. Group 27 is the size your Casita came with and will fit all Casitas. Group 31 is the max size (Casitas optional upgrade) and needs modifications to the battery holder to fit. Wet Cells have a higher capacity and are cheaper but need the water levels topped off eery 6 months. AGM are maintenance free, but cost a little more.
Trojan 27TMH deep cycle wet cell – $200 installed
Trojan 31HXS deep cycle wet cell – $210
Trojan AGM27 or AGM31 overdrive deep cycle – $275