battery and perko question

I have dual batteries with a perko switch, one is a regular car battery and the other is a deep cycle. I understand that the deep cycle is designed more for chilling and listening to the radio with the engine off but I hardly ever do that. I think I would prefer to be able to start off both batteries so my question is should I replace the deep cylcle with another starter battery? Also, the perko switch can be set to battery 1, 2 or both. If I put it on both will the alternator keep both batteries charged?

i ran 2 starting batteries and it worked just fine. both will charge if it is set on both

Yes as stated above when the switch is set to both the alternator will charge both batteries.
I would say that if you really want to stat off of both batteries then why have 2? You could just get away with one battery. Usually you have more batteries for keeping your starting and house banks seperate, or having a back up just in case. I would recommend that you while your driving leave the switch set to both. When you stop set it back to one. You could always add a Automatic Charging Relay. I would say thats it is alot "safer" to have a backup battery then it is to have a larger starting bank.

Yeah I hear you on it kind of defeating the purpose of having dual batteries if I go with two starter batteries. I guess since I don't really have much use for the deep cycle I was just trying to figure out the best set up to give me the added reliability. I go out on a fairly remote river and it is not uncommon to be several miles away from the ramp so I am kind of paranoid about getting stranded.

You can still start off a starting & deep combo no problem. You won't gain anything by going to starts.

Your deep-cycle will start the engine with no problem if needed. If the main starting battery is run down, or takes a crap, switching to "Both" will cause the good battery to try and equalize with the run down one. So just use position "2".