Just to elaborate on roady's answer
From my notepad:
3/12v = 36v?
Or can I use 3 12v batteries in my 36v golf cart?
You can use 3/12v batteries in series to create a 36v power supply. However this supply will be lacking in amperage capacity and deep cycle ability. The result will be poor run time and shortened battery lifetime.
The batteries should be golf cart specific batteries.
Golf cart batteries are designed to hold a large amount of amperage and to be discharged relatively deeply as opposed to the shallow discharge and immediate replenishing routine of cranking batteries.
Automotive batteries do not store as much amperage and are designed for shallow discharge and immediate recharge. Like starting a car and having the alternator immediately begin charging.
You can connect 3 automotive 12v batteries in series and get 36v. You will not the amperage reserve or operational characteristics needed to make the batteries perform well or last satisfactorily in a golf cart.
I hope this helps ...