Re: What type of battery?
Whew, deep breath here.
You need a marine cranking battery for the motor, deep cycle for the electronics. You said Galaxy so I'm assuming no trolling motor so unless you have the stereo from hell, you aren't going to need a giant deep cycle. A 115 Johnson is not really going to require a huge level of cold crankng amps (yes, I know I'll get beat up for that), and most marine cranking batteries will be adequate.
I have a Walmart Everstart starting battery for my 60hp Merc 4st that I bought in 2008 and is doing the job fine. My deep cycle is a Diehard, also bought in 2008 and doing fine. I would have bought a Walmart deep cycle but when I killed my old dc battery (batteries don't die, they are killed by their owners), the local Wally world had no deep cycles in stock.
I haven't priced batteries since 2008 so I'm not sure where they are right now. As near as I can remember, The Walmart battery was around 70 bucks and the Sears around 90. You most definitely do not need a $300 battery.
FWIW, most of the batteries out there, whatever brand, are made by JCI or Exide. They both know how to make batteries.
Just to add, when I bought my boat new, it had Interstate batteries, cranking and deep cycle. The cranking battery lasted 7 years. It was actually still starting the motor easily, but was only getting to 12.1 volts fully charged so I got paranoid and swapped it out. I killed the deep cycle 2 years in, long story.