Use 24v Batteries to run 12v System... Possible?

PS: others have commented already, but in case if it wasn't clear, that your idea -

"I could use 1 or 2 smaller batteries & due to you only needing to pull 1/2 the amps @ 24v's"

- this is like using bottles with a wide neck vs narrow neck. It doesn't change the available amount of water.

The only way to have a physically smaller bank with the same amount of energy, is to use Li batteries.