Battery Charger

[oldcat]

I have read some old posts, but am still unclear on a couple of things. I bought a 15 amp charger I want to use when I have a night with shore power between stints of dry camping. (My converter only puts out a small charge). I have two 6 volt batteries in series.

Do I need to install a cutoff switch between the battery and converter to isolate the batteries when charging? What about when I use the desulphating mode? When charging the 6 volt batteries in series I set the charger to 12 volts, right?

Thanks in advance.