I agree with Marty on the batteries. I use Interstate Economy batteries in all my vehicles. even my 6.0PSD which takes a ton of power. They are ~$50 at the the Interstate Battery store. I think at this point I've bought almost a dozen of these. Not because they fail quick..... they last as long a the expensive ones, I've put them in that many vehicles. I am on the 3rd set in my diesel, but if you get much past 4 years on a set in a 6.0 you are extremely lucky (I've has the 6.0 for 13+ years, that's also why I am on the 3rd set).
For garden tractor batteries, I get the ~$20 from wherever, Wally-World, Orschlein, Auto Zone, Big R..... etc. They seem to last 3-5 years for me, however, my tractors stay in the attached garage (if they are in the barn. it's for longer storage and they have no fuel (run till stalls) and no battery) and it is fairly climate controlled. The furnace-A/C is in there , so it stays warmer in the winter (mid 50's+) and in the summer cooler than outside. I can normally hop on, and hit the key and they fire right up, summer or winter. At Dad's a garden tractor battery seemed to last maybe a year. But his garage/shop is not climate controlled. It's a corrugated steel building, so it's hotter than h**l in the summer, and a deep freeze in the winter (East Central Illinois). Several years ago, he started using a "battery tender" (not the brand, the concept) and the batteries are lasting much longer now. Go out, hit the key and they fire up. He even uses one on his car that doesn't get driven much. I have one here for which ever vehicle is "off duty"....... that seems to help a bunch.