Most all motor homes do indeed have two batteries.. One (Called Main, Chassis or Engine) battery is for the "Truck" part of the vehicle.. The engine, Headlights, marker lights, tail lights, and such. if you had a same length box truck this is the battery that would power everything on that truck that needs power.
The other (HOUSE or AUX) battery system is responsible for the "House" part, Water pump, LIghts, Water pump, House radio (if of the dash type) control power to the fridge, Air Conditioners, furnace (Also operational power) and water heater.
You have either a converter (Makes 12 volt out of 120 volt converts AC to DC) or an inverter/converter.. These make 12 volt DC out of 120 AC (convert) and make 120AC out of 12 DC (Invert, the inverse of conversion) when needed.
If you have a converter, you may also hae a seperate inverter (usually a small one that runs the main entertainment section)
Though some RV's use "Marine/deep cycle" batteries, whihch are the worst of two worlds (Starting and very slightly deeper than normal cycle)
Many motor homes come with a pair of GC-2 size Golf Car DEEP CYCLE batteies. (much better)
Some.. Well there is one poster in another forum who is asking for options changing out his batteries.. 700 dollar a pop 8D AGM Deep cells.
now.. I will say I wish I could afford that kind of battery power.. (I can't even CARRY that kind of battery power in this coach)
Folks here like to ask which is better 2 sixes or 2 12's... I keep telling them "NOT ENOUGH INFO" here is why.. Each of those 8D's is bigger than the standard six volt pair.. So two of those is clearly better.
Two Group 24's however.. Well a pair of sixes is like 3 1/2 Group 24's.
