Cold starting our 1982 Ford 4610 diesel tractor on a 47 degree morning

This is our 1982 Ford 4610 tractor. It's a two wheel drive, has a loader that we put on it which is made for a different ford, but it fits ok after some modifications. It's a very loud 3 cylinder diesel that idles nice and slow like you don't get to hear engines do much these days. This is me starting it while waiting on my dad to get something from the house before we moved a bunch of round bales from one place to another with it. It was about 40 degrees outside and I had my Galaxy S4 phone in my coat pocket. we think the battery on the tractor is getting weak, not cranking very fast, even for being cold that's still too slow, and it should have had to crank that long, that cold or not. Probably not making as much heat with the compression stroke happening more slowly on account of the slower cranking. Anyway, I love listening to this tractor idle. I have to turn my hearing aids down a bit though because it's pretty noisy, but I could practically sit there and listen to it run like in this recording all day long! Plus the diesel smell is like a drug on a cold morning like this. My poor, poor brain cells!