Old Batteries

I’m examining our electrical system. Our batteries seem in need of replacing, as they are 4 years old. I think we will limp them alone for the next 6-month and watch for sales. I estimate our capacity at 160 amp-hours but I think I would like to double that. We took some measurements under the back bed and I think we could fit some AGM batteries under that space. AGM batteries are more expensive about twice the price but do not require a vented space. We’ll look into if we could build more vented space but I think the AGM batteries will be the considerably simpler and maybe even cheaper answer.