You don't mention if these are deep cycle batteries.. IMHO, if your getting
them at Sam's Club, the chances are that they are automotive with the
"Marine" or "RV" label..

If this is true then the two years heavy service you got out of them is
about all you can expect. The main performance difference between
cranking/automotive and true deep cycle is the vast difference in the number
of "Deep" cycles.. The deep cycle batt. can handle hundreds while an
automotive will be less than 100. Battery mfgs don't advertise the number or
cycles unless they can claim several hundred cycles.

If your running refrigeration, you should invest in true deep cycles because
of the frequency of lowering the battery charge to less than 50%.

Sams Club does sell a 6volt golf cart battery that bares a striking
resemblence to the Trojan T-105 but for a little less.. I'm not sure of it's
performance rating..

If you invest in deep cycle batteries, then you can further improve their
performance by getting a good 3 stage battery charger that allows for an
absorption charge periodically. I think that is what you were refering to as
"de-sulpher...".

Sorry to say, I think your existing batteries have seen their best days.


--
My opinion and experience. FWIW

Steve
s/v Good Intentions