michael, Welcome to jd Fanatics. Is the charging system is operating properly, when the tractor should have keep running. If your charging systems has issues, then when the battery gets weak it will cause the engine to die. Did it start missing or back firing before it died? The battery can have enough charge to keep the engine running, but not enough charge to start the engine. Good Luck.
How old is your battery? These tractor batteries are only good for about four years. Also just to note, you don't want your battery sitting on a metal surface. If possible, use a piece of rubber between the battery and the tray. It will aid in keeping your battery charged and ready to go, as long as your charging system is up to snuff.
Does the tractor have a standard starter, or a starter/generator combination? If starter/generator combination, you may look into getting it checked so you can feel at ease in knowing that it's putting out the amps that are required.