Helping a neighbor today with his John Deere 6400. His battery is going on about 8 years now and he wants to replace it thinking that it is about at the end of its life and he doesn't want to have problems 6 miles from his home base. Always has been pretty hard to start in the winter without jumping it. His current battery (group 31) which is not to original tractor specs has about 1000 cranking amps. He was told that the tractor requires a special battery with around 1200 cranking amps in order to get it to spin fast enough to start. Just was wondering if that was to build the required compression or is it something to do with oil pressure or the injection pump. Went to a farm store selling Interstate and Deka batteries today and the owner of the store sort of verified the fact that the 6400/6420 required a special battery as his two sons each had a Deere 6420. Sounds like his sons put cheaper 950 cranking amp batteries in their tractors and keep them inside in the winter. Store owner said Mother Deere possibly has a $300 price tag on that specific battery. Maybe the bigger battery is recommended because it is just a single battery setup. Thanks for your thoughts.