had to put 2 new batteries in the Dodge diesel last winter, one battery was doa the other had some good left in it but ya got ta have both of em to crank that diesel, the diesel generator, I change every 2 years, keep the old battery for the diesel loader, i can put a charger on it and make it last another year or so. The 2 diesel tractors have 1 battery apiece but they still have the original in them. the Toyota still new. I try to keep at least 1 extra battery for the loader, it's old and sometimes it drains the battery between uses, try to keep a charger on it when it sits.
got a set of Jumper cables though that will jump anything if you got a battery, 1/0 cable with the good brass ends, 30 feet long. had to jump the generator once, in the winter, it was just barley above zero, I got a tractor started hooked up the cables and let it charge for a few minutes and hit the starter, cranked right up. made that $100 for the cables seem cheap.

sure wouldn't take for em.