"3 golf cart batteries to put in serial"
I believe you mean series? Are these 6V or 12V batteries? If they are 6V, putting them in series would give you 18V, if they are 12V batteries, then you'd have 36V in series. Either way, that is excessive voltage.
If you are using 6V batteries, put two in in series to = 12V. If you want more than two, you'd have to use at least 4. For a four battery (6V) set up, you'd have two banks of two batteries set up in a series/parallel combination.
If you are using 12V batteries, put them all in parallel.