1. As mentioned, 85-100 AH is the range for 27s
2. Check the date codes on the batteries. It's good to know how old they are. Some dealers do not install batteries until the RV is set up for delivery. Google will help you determine what the date codes mean.
3. Remember that you do not want to discharge the batteries beyond 50% state of charge. 35% is a better rule for so-called "Marine/RV" batteries which are not true deep cycle.
4. You can "Play around" with the batteries that you have now, but some true deep cycle batteries are what you will probably want in the near future.
2015 T12RBST Flagstaff Hardside
2008 Itasca Meridian 37H