Originally Posted by JayArras
Without being recharged, or total # of years?
As a general rule, it will depend on how often charged, how well maintained, what's connected to it, etc.
As well as type of battery that's utilized as a house battery
Starting battery (cheapie from Walmart) Not very long
Marine Deep Cycle A lot longer
Pair of 6 v golf cart batteries, longer still.
"Lithium" A really long time.
That's just their lifetimes assuming they are charged regularly and discharged according to recommendations for each type.
It's also going to depend on how well matched the battery bank is to the average load placed on it by the RV. If the batteries are continuously run flat when the furnace runs overnight, you need more battery capacity.
If you rarely go below 50%, the batteries, even plain lead acid deep cycle batteries will last many hundreds of cycles. Now divide the number of camping trips you take per year into an average number of 800 cycles for a lead acid deep cycle and you have the number of years you might expect.
Many variables so you have to start with YOUR parameters and work from there.
Every deep cycle battery manufacturer will publish their data on how many cycles based on depth of discharge. Now plug in your requirements.