I have one cranking battery for my motor and two deep cycle for my trolling motor. I would like to hook another battery to my cranking so Ill have more running time on my live wells and fish finder.
Do I hook up the positive to the negitive or positive to positive?
Do I hook up a deep cycle or cranking battery? After a long day of fishing the aireator shows signs of weakness and when it kicks on my graph fades in and out. I think it is to much draw on that one battery.
Can anyone help?

If you were to do this, connect the positives and negatives together so they are hooked up in parallel, 12 Volts (versus in series, 24 Volts). However, do not hook together a deep cycle to a cranking battery, very dangerous. You shouldn't even hook up a new and an old battery together.
If I needed more juice I would buy a deep cycle battery and run my live well and electronics off of it. Leave your cranking battery for just your motor and then it should provide enough power.