batteries in series add the voltages together, and each battery sees the full current.
batteries in parallel add the amperage (current) together, the voltage of the whole is the voltage of any one member.
2 6V batteries are connected in series to provide 12 volts.
the standard size 6V golf cart battery that fits in our Escapes is known as a T105 or a GC-2 (same difference). These can be had as flooded or AGM (absorbed glass mat).