I definitely agree with the above comments re: getting a bettery battery. I hope my info on the desulfators (which was meant as a general info posting for when people find this thread) wasn't taken as arguing against the fact that starter batteries make bad deep cycle batteries. Marine combo batteries are slightly better than, say, automotive batteries for non-crankiong discharges as they're expected to run loads like bilg epumps and such when the engine is down but there's no shore power, but they're not designed for longer duration deeper discharges or the longer idle periods that trailers/RVs suffer through, especially in off the grid camping. The generic group 24 combo batteries 'work' but their biggest advantage is they're cheap and available at any big box store or car parts house. The downside is you definitely swap them more often and the conditions which will kill them are much easier to enter than for better quality batteries. If you have a coach that can handle the weight, flooded deep cycle batteries will last the longest of the traditional lead acid style (if you can prevent them from freezing or drying out during charge/discharge, which are their most dangerous conditions), followed by the sealed long duration AGMs (which can handle unattended periods and freezing temps better), then high quality true deep cycle general lead acid batteries, then you get to the generic deep cycle, then combo, then starter batteries. The cost per battery is higher at the upper end but the lifespan and endurance of each is also much different than combo or starter batteries, by multiples of the usable capacity of the combo or starter batteries.
If you own or can borrow a battery already and it's recoverable then desulfation can be worthwhile to give it a shot, was the only point I was aiming for
And if you have other batteries that might sit or which you want to max their lifespan and have not had a good charger to use anyway, then you can still use the charger/desulfator in the future (even on new batteries) which might make it a good investment. Mine get used constantly, either on my own not-in-use batteries or where folks borrow it to recover batteries their charger can't bring back or replace the capacity their chargers aren't able to get them due to plate surface conditions.