I bought a wally's schumarker brand charger which has a desul, charge, voltage option.
Here is what I did to improve my 2007 honda ridgeline battery that barely cranked in winter and the truck sits most of the year.
first I charged the battery in normal charge mode,
then I ran the desul mode 2x times back to back. this was 3 years back and the battery is performing better and stil working.
I spent $45 for the charger I think, they are more now, like $55.
on the flip side, I had an optima blue in my Grandby truck camper, and it was low.
I bought a dedicated AGM batt charger and followed the steps provided by optima to revive the battery, no dice, I just wasted 70 for the charger and more for the battery.
I am actually trying to revive a deep cycle battery I pulled from my toyota winnie camper,
one side has a bulge, which is not good, still I want to see if I can revive it.
what is the volt reading on the battery?
trickle charge it to voltage first then charge with high amp and then run desul.
good luck!