Depends on what your needs are. If you dry camp then buy the batteries that offer the greatest amount of amp hours available. (6 or 12 volt) If you camp with hookups then no need to go expensive with batteries. We choose a pair of 6 volt golf cart batteries (Trojan) as we dry camp a lot. Good luck with your new rig!
If you have the vin number you can to the RAM TOWING site and enter the vin number. This will give you the specifics for your truck. Good luck with your new rig. you can look it up under the "look up my vehicle" section.
You could try disconnecting them while plugged in to your 7 wire. See if it works before you move the 5er. I also have the hyd gear and slides. I have not tried to operate just on the 7 wire. Good luck.