When you say stops , does this mean the charger cuts off or that it just stays at 6.5.
If the cart has a OBC or a intelligent charger then it can take up to 16 hours to charge Batteries, then the charger should shut off automatically.
Do what roady89 said then
Give the charger 15 Hours and see what happens.
30 minutes after charger is removed check pack Voltage with a Digital Volt meter and post results here .
Read this
http://www.buggiesgonewild.com/elect...-readings.html