Advance Auto parts stores sell batteries for lawnmowers, ATVs and small vehicles like golf carts. They are cheaper than going to AutoZone or Nappa and their warrenty and return policy is better too.
Depending on the voltage that you want for your golf cart will be the first start. if it is a six volt battery then I would recommend the trojan t-105 batteries. If it is an eight volt battery you are looking for then I would recommend the trojan t-875 battery.