I too think they're talking about Group size. A single group 24 will run down in a hurry and if you don't have LED lighting and and are not plugged into shore power the lights can run it down quick. I would verify the Dealer is planning to install two group 27 or 29 batteries. If they continue to talk 24 volts or 28 volts, Call Redwood right from their Service Desk and have them talk to someone at RW to set them straight. I swear that some Dealer Service Depts, the Techs have to look at their name badge to spell their name. Shame we as Customers have to educate them, but better that than leting them do something that will seriously damage your Rig.
Michelle & Ann
2018 Chevy 3500HD Crew Cab High Country DRW, D/A, 2016 RW39MB, Dual ACs, Auto Level, Auto Sat Dish, Stack W/D, King Sleep #, 17.5" Sailuns w/Disc, MORryde IS & Pin, Comfort Ride Hitch, 5.5 Onan, Res Fridge & Induction Cook Top