Engine Battery question

[Leftyclick]

I'm not sure this is the best place to post this question, so forgive me if I'm in the wrong place.

My 1989 Ford B-700 (7.8l Diesel, Wayne body) has a battery compartment with 3 large batteries used to start the engine. My question is, is that really necessary? I grew up on a farm and we had a couple of pretty large tractors that only used one large battery. Given they had almost no electronics, but I couldn't help but wonder about it. If I could step it down to one battery I could use the space to store batteries to run my solar set up there, eventually. Does anyone have any recommendations on how to proceed?

[frank-id]

Batteries and size and number of batteries is usually selected in relation to the actual service of the batteries.
School buses usually have some back up power for buses based on the passengers on bus. Most big bus engines will start with about 2000 amps. Considering cold weather and other conditions, often there is about 3000 amps available for starting. Lites and any other electrical requirements also are a big demand on batteries. The alternators have the ability to recharge the batteries quickly. When building a RV from a school bus, the same demands are not the same.
Many buses are started with 2 batteries with 8-900 cca. The care and feeding of batteries is very important. A battery
that indicates 12.0 volts is 75% discharged. A full battery should reflect 12.6 volts. The battery connections are very important. There are many battery methods for connections. Frank