House battery size

Fully charge them and have them LOAD TESTED. Free at any place that sells batteries.

That will tell you if they are good/bad.

Much of "what batteries to use" depends on the configuration of your battery tray/area.

If it will accommodate them, 6 VDC golf cart batteries wires in SERIES to make a 12 VDC battery is usually the least expensive way to get quality deep cycle batteries. The come in different heights as well as other dimensions, so depends on what will fit.

As to how many/total amp-hrs, that really depends on how you use the coach. If mostly RV park to RV park VS lots of boondocking-- the answer will be different.

I currently have two 12 volt batteries connected together. When new, coach came with one 12 volt battery. Subject came up because full wall slide seems slower coming in lately. Voltage is good but dont know about during load.

Doug

You have a 2006 Fleetwood? So, since the unit is that old. AGM and Lithium are not used in your application due to the TYPE charging system used in 2006. You would have to upgrade your Coach 12 volt charging system to use AGM and Lithium. That leaves 2 choices. 12 volt, 27 series RV deep cycle batteries, or 6 volt RV deep cycle batteries. BOTH were used 20 years ago. To determine if 6 or 12 volt is easy as long as you have the Coach batteries still installed. 12 volt batteries have 6 fill caps. 6 volt batteries have 3 fill caps. Even sealed maintenance free will show fill cap holes. Doug