Battery question(s)

[FroggerZack]

I have a 16 ft Tracker boat that currently has two batteries, a starting battery and a deep cycle that are wired in parallel for my 12v trolling motor. Although it is not optimal I have been running this configuration for about 3-4 years for extended run time on the trolling motor and has been pretty good up until now. I went fishing and noticed that volt meter on my depth finder was going down quicker than usual and finally was just barely able to start my engine to get in! I swung by Autozone on the way in and had the batteries tested and the starting battery was bad.

Should I replace this battery with a combination starting/cranking battery or just a plain starting battery? I don't really have the money to pony up for a couple of batteries at this point but putting in a couple combos would be sweet!

Whats a good brand of battery? I was thinking about going by Academy as they are real good about returns and such if I have a problem.

Thanks guys for your help.