Choosing a battery bank size for your RV is crucial in having enough power to go off grid camping. The first thisng to consider when sizing your battery bank is to determine how much space and weight carrying capacity you have availble. Most battery types are heavy and take up a decent amount of room.
Some batteries will require outside venting: Please see our Battery choices and types for mobile solar arrays article for more information on choosing the right type of batteries for your RV.
Many Travel trailers will have the batteries on the tounge which limits total number and can create an extremely heavey tounge weight. Other batteries are loacted on one side of a camper and can create an unbalanced towing situation.
Once you are able to figure out how you can install, mount and safely operate batteries in your RV it is time to determine battery bank size. Most RV applications operate at 12 volts so you will most likely only parallel battery connections between them. Deep cycle marine batteries are rated in amp hours when they are designed for deep discharge. The amp hoor rating of most batteries allow a user to estimate how much power a battery contains. The actual useful power depends on battery type and drain rate or the speed at which you draw power from the batteries.
A higher drain rate will drain more power than a lower drain rate. Even if your load is only 2X as much, you could actually reduce the power in the battery by 3X or 4X as much depending on load.
You want to keep most battery banks charging as much as possible. This keeps them topped off and running properly. This can be acomplished using your converter & generator, grid power, or rv solar kit.
These each offer different ways to recharge your battery bank. If you have a really good RV solar system. You can get 30 amps of charging in the full sun. In a 10 hour solar day you could have 300 amps of charging power. Having enough battery bank to handle a 10% charge rate would be ideal. For example if your charger is 30 amp, an ideal battery bank would be 300 amp/hours. While it may be hard to always acheive this, try to shoot for a 10% charge rate if weight, budget and space allow.