In a motorhome, you have "House batteries" and you have the normal battery used to start the vehicle.
Some motorhomes use two - six batteries as "House Batteries".
Depending on how they are wired, you will get longer time running your interior lights, microwave, fridge etc, etc......
You will still have 12 volts DC power, but more current or power to use accessories longer.
You can do the same in any trailer. If you do a lot of "Boondocking" or "Dry Camping", you will want to have more than one battery because you are not connected to shore power.
If you would like more details, please PM me. I can give you more info.
Former electrician and currently an electronics technician.
HAPPY CAMPING!! :D
Daryl and Sandy
2013 Eagle 314BDS
2012 Ford F150 Platinum, 4 x 4 Crew Cab with Ecoboost