Hello. I recently purchased a 1999 240 Sundancer. Enjoying it very much. I have a question about the batteries. I have the switch with positions for battery 1, battery 2, or Both. However, in the engine compartment there are three batteries. I assume a previous owner added a battery. Not sure why. I don’t know a lot about batteries, but it appears these are wired on a “parallel” manner which apparently might increase run-time? Mainly, i’m Wondering how the third battery interacts with the battery switch e.g. is the third battery utilized only when the switch is in the Both position? Will the alternator charge all of the batteries? What is the most effective way to take advantage of having this extra battery if I’m away from shore power for a few days? Thanks for any help!