I don't disconnect the battery nor put it on a charger. I leave the RV hooked up. The converter in the RV has a built in float charger that works just fine. You might check yours. My last RV (2011 CF285RL) was 2 years old and with the original battery when traded in. No problems with it. I added water to it twice in 2 years so I know it wasn't overcharged.
I use the Battery Tender's on everything else. Welder, generator, etc..
Clif and Millie
Ozzie (half a dog tall & 2 dogs long)
2009 Ford Lariat F350 SRW CC Diesel
2013 Cruiser CF305SK Patriot Edition