Re: SM Batteries
I don't know where you are planning on getting your batteries from but I highly recommend that you check this local Annapolis place for before you buy anything: https://www.stevensbattery.com/
The owner is a boater and very knowledgeable. They have great customer service and pricing. They have a ton of batteries in stock but they turn them over quickly. Last year I purchased 12 x Deka Marine Master DC31DT for a lower price than I could find anywhere on the internet when factoring in shipping cost - somewhere around $120 each. I bought them in September of 2017 and the stickers on them show that they were manufactured in July of 2017. They also load tested each one of them for me before loading them into my car so I knew that I was not getting a "dud".
Last, they let a friend of mine borrow some empty 6v battery cases so that he could mock up his battery bank to see how many batteries he can fit. They would likely let you do the same if you asked.
SM #440 Cara
Deale, MD USA