Humm. Diesel.. now some Diesels (most of the RV ones I suspect) Start off the battery.. But I do recall in days of old when Truckers were bold they had Air Start diesels.. yes, compressed air started them.
IF this is the case there should be a standard "Tire type" valve somewhere on an air manufold.. That's how you do it.. Alas, I have no clue as to where.
Now to tell which you have. Listen to a neighbor start his Diesel. Air starts are VERY VERY NOISY compared to electric starts.
Finally, You may have goofed on the battery install.