Good Luck! We have a 70's vintage CAT tracked loader on our place that has been a continual pain in the a--. Be prepared for sticker stock if you buy CAT branded batteries (or any CAT branded product really). Also the batteries are HEAVY, ours weigh 80 lbs each and you have to lift them over the tracks to get them in the compartment.
Ours has a manual primer pump that pulls diesel to the front where the pump does not have to work as hard at start up. I'm not familiar with the D7, but if it has glow plugs be sure and let them do their thing for at least a minute or two before even attempting to crank.
If this machine does not have hydraulic transmission or lift cylinders, consider yourself lucky. Hydraulic seals are our biggest problem.
Here is a link to a forum full of good info about old heavy equipment:
https://www.heavyequipmentforums.com/
This is a link to an online supply house that has the best pricing I have found for our machine:
https://offroadeq.com/
Mike Pearson