48 club car short battery life

[Jblack]

MY buddy has a 02 club car that will not hold a charge. New batteries 3 three years ago, 6 8volt batteries. He has maybe 10-15 total hours on it. This thing will not hold a charge for more than one day,or around maybe 10-12 miles. It has a 5.5hp motor. Not sure about the controller. Now it is heavier than most, it has the H1 hummdinger body,lift kit, 23 tires. When it
s fully charged it runs great.
What is the first thing to check out, a diagnostic test to run to figure out what is going on. Just need to get some advice to trya nd figure out what's wrong...batteries, cables, some other component. I'm a gasser guy, so I don't know a whole lot about electric carts.

Thanks
John