Golf Cart batteries
Nope, not a good idea to discharge any battery below 50%. Doing that even once substantially reduces the life of the battery.
Having said that golf cart batteries have thicker plates and are a bit taller than conventioal batteries (group 24,27) and this makes em idea for deep cycling.
There are many different sizes of golf cart batteries, not just the 220 Ah standard ones. Also you can get AGM and Gel batteries in a six volt golf cart battery config. Good luck with you choices. Ryan