If I am going to have a power source available, do I need a full battery pack?

No, you can have down to 6 batteries. Although there are important concerns to consider: A 1200 Ah battery pack adds 1100 lbs to the base of the trailer. This is a key consideration to the stability of the trailer in higher winds. The system is designed and is technically balanced for the 1200 Ah battery banks. In addition, all charging and battery life estimates are based on a 1200 Ah Battery bank.