Battery and drive question

[BigDog]

The other night I checked my battery voltage with a volt meter. It read 36.17 volts. I drove the cat(2005 ezgo 36v electric,txt, pds) about a 1/4 of a mile. Stopped for a moment and tried to go again. Would not go-acted like the batteries were dead. Checked the voltage-34.63v. Tried to go fwd or rev-no luck.. Walked back to the house, got a tow rope and the pick up and towed it home after switching the tow/run switch to tow. Left it parked overnight, with the key off. Went out the next morning, checked individual batteries(6.16v or better) and the total charge(34.16v). Turned on the key, put it in fwd and it drove fine! As I am new to electric golf carts, am mechanically inclined, could someone give me some direction of my problem please?