I did a test of my 11 year old Interstate 27 starting batteries before replacing them . Each by it's self would start my ISL and each load tested at 50% of their 1000+ CCA. Two 8D for starting that small an engine is absurd but it's your money. Because I was able to keep my old batteries I did buy new and put the old in a machine at home to see how much longer they will last.
* I did have some fun. With the Interstate rep when I asked that I needed some helpf deciding to go back with their battery. He asked What's the problem? and I answered they are only 11 years old. :B