We had that same chassis /engine set up. After sitting for a while, the engine would turn over, but was reluctant to start. I could put a single jumper cable from the house to the chassis battery and it would spin much faster and start the engine. I ended up replacing the chasis batteries. Whether or not this is your problem, I cannot say, but it worked for me.
Also had a MF tractor that would not start and held a gas soaked rag to the breather while the engine turned over - cranked right up. Might not be a good idea on yours since there is a heating grid in the air system on the Cat.