Batteries can fool you. You can check voltage. and it will be right. You can check chemistry etc. However the most definitive check you can make is a test under load, in the cart.
You will need a VOM with long leads and alligator clips on the leads.
Pick up the seat and clip to 1 battery
Put the seat down
Accelerate the cart and note the voltage drop. Chart it.
Repeat with each battery.
If you have a dud it will show up big time.
This test works with ALL types of batteries