I'll be replacing the battery in my fairly new NH WM25 later this year. I think it most economical to replace car and tractor batteries every 3 years before they fail, so I never incur extra expense or other losses because the machine won't run, but that's just my opinion. I also think autumn is the ideal time, because summers are hard on battery lifetimes, and winters are the most challenging time to start the engine. That is, summer does the most harm, and winter requires the best battery. Best to let the final summer make the battery as bad as it will get, and then start the challenging winter in strength.
I plan on getting the highest CCA that will fit the bracket and the cables. But some brands must be better than others. What are the good brands and what brands should be avoided? And is it better to shop at TSC, or the tractor dealer, or an auto parts store, or a chain store like Sears (if any of those are still around next fall)?