Not sure what brand batteries or on his cart, but the average with well maintained batteries is 6-8 years. If you use the cart often, you should check the water in them every month. A smart charge will keep them balanced and conditioned. I am sure the cart has a smart charger and more than likely trojan batteries. A new set of batteries can run anywhere from $450 to over a $1000 depending on brand and amp/hour rating. I have batteries from Sam's in my cart and they are 2.5 years old with no loss of performance so far. Hope this helps.
What's the life span of the batteries and how much do they cost to replace? Thanks.