I have a 2011 Ezgo TXT 48 volt. 
A few weeks ago it started jerking when we would be riding around the facility (I'm the manager of a storage facility so its just used within the back area when checking/cleaning/showing units). When you press the gas pedal it will go but it jerks every few seconds and will go so slow its almost a crawl and you wonder if you will make it back to the shed. A customer had a volt tester so he checked the batteries and found one was not holding a charge at all. I replaced that battery. When I went to charge the cart I get 2 red blinks and the side says that means Battery Voltage Fault. I took the charger over to another location to verify that it would charge which it went green on another cart no problem. So today I got a battery charger and a volt tester. We charged all the battery separately to showing at least 8.15 (had been showing in the 6's) on the tester. I tried plugging in the charger still flashing 2 red lights. We road it around one time (less then 3 minutes of ride time) its still jerking I test the batteries when we got back to the shed they were all ready in the 7's, charger still showing 2 flashing lights.
Anyone have any ideal what else my mom and I can try? Or what the issue could be? Any help would be greatly appreciated cause these two girls are totally out of our knowing what else to try element.