Some people dont store their equipment inside. Good luck starting it at 0 especially if the engine has wear.
Case covered that issue by telling people in the Op Manual to change their oil for the winter time if extreme cold conditions are normal in your area. The engine oil on a Kohler or Onan can be swapped out for 0W30 synthetic and the hydraulic oil can also be changed to a synthetic such as 5W40. When people have a hard time starting their cars in the winter, then the smart ones do things such as install magnetic oil pan heaters or dipstick heaters or battery warmers. They can also toss a heavy tarp over the entire tractor and put some form of electric heat under it that can be controlled from inside the garage whenever use of the tractor is anticipated.
Using a car battery with 900 cold cranking amps certainly helps to make sure there is enough power there to spin the engine over but all of that is predicated on the starter motor or start/gen being in good condition. Back in the day when I worked in Service Stations, customers brought their cars in for a fall tune up and then a spring tune up. That is no longer necessary today with the modern ignitions systems but people seem to forget that most Onan and Kohler engines in these tractors date back to that era. They need attention to make sure they will light up when they are spun over just a few revolutions. The guy I use to rebuild start/gens etc has been doing it a long, long time and has seen many of them badly damaged thanks to being spun constantly while trying to start an engine that was badly out of tune.
If Colt, Case or Ingersoll felt that these tractors NEEDED a 900 CCA battery, then you can be sure that they would have put one in. If the engine is badly worn, then rebuild it. Applying band-aids won't fix anything.