RV and Marine Batteries
These batteries are often advertised as a compromise between regular car batteries and the specialized deep cycle batteries required for a solar electric system. However, plates in these are more similar to the regular car batteries. They are not built to withstand the deep discharging (discharging your battery as much as 80%) that you will really need.
What's more, a marine or RV battery may be labeled as "deep cycle" when it is not.
How to tell the difference? Any solar batteries that are not a true deep cycle battery will be rated for its CA (cranking amps); this can read out as CCA (cold cranking amps) or MCA (marine cranking amps). Two companies, Rolls-Surrette and Concorde, do make a true deep cycle marine battery. If maintained properly, these will last many years more.
Other (Better) Options
You can keep two separate batteries-a regular starting battery for your RV's engine and a separate deep cycle battery for your solar electric system.
Some solar RV users recommend purchasing a deep cycle battery and using it as your starting battery. The deep cycle battery may not have the "cranking amps" needed to get your RV started (especially on some mornings). However, you can compensate for this by over-sizing your battery at last 20 percent, in order to get the starting energy you need.