Charging 2 marine batteries

[Triton195CC2006]

I was told it’s a good idea to charge your deep cycle batteries while storing it during the week. I recently purchased a battery charger and wanted to get some tips on using it. what should the set up be?

on both
on #1
on #2
off

I have bought the BLACK+DECKER BC15BD 15 Amp Bench Battery Charger 40 Amp Engine Start Alternator Check

 

[Faztbullet]

If the rocker switch is still connected and functional on boat you want "both"