You store energy (watt-hours). You put it in and take it out as power (watts) over a period of time.
How many batteries depends on how much energy you plan to store, or use. How many watts do you need to draw from storage, for how many hours? Different types of usage have radically different answers.
Most small RVs store 1200 to 2400 watt-hours, e.g. 100 to 200 amp-hours at 12 volts, with the expectation of using no more than half of that during one charge-discharge cycle, which might be a day. Using more than half the batteries' capacity greatly shortens the number if cycles available.
Larger RVs running a number of large electric appliances from stored power may store 4 to 10 KW hours, might have 400 to 1000 pounds of lead-acid batteries to do that. But then they need much larger charging systems to keep those up, or need to be charging for long periods of time.
You need to figure out your own electricity use and storage goals.
My need was for marine (rather than deep cycle) batteries, because I have some short-term high amperage loads, but I passed on the DieHards. Those were priced way higher than equivalent batteries from discount stores, auto stores, and even the overpriced Interstates at RV and boat dealers. If you have smaller loads over a longer period of time, you should look at golf-cart batteries.
A consideration for me is package size. You might get the same capacity in four 60 pound batteries, two 110 pound batteries, or one 190 pound battery. Fewer bigger batteries can save you a little weight (and sometimes quite a bit of cost), but what can you lift and wrestle into the space?
