If you hook up your solar panel positive lead to battery 1 and negative to battery 2, it will only charge battery 1 unless you put your switch in BOTH. The best way to do it, as Todd says, is to install a battery combiner that automatically connects them both when a charge voltage is available. It doesn't sound to me like there is any concern with the way your 1/BOTH/2 switch is installed. The way you describe it is the way mine works.