First of I have a 55 lbs thrust "older" Minn kota Extreme w/ maximizer trolling motor.  This is my only means of propulsion for my two man boat.  

Right now I have a Auto Craft battery ........ Group 27, Reserve Capacity 175 min ( I can get more specs if needed, I know nothing about batteries, but I always hear people talking about these numbers ).  Last year was the first year that I think I ever maintained my battery correctly .... mainly charging right after each use.  And I really saw a difference in the length of time my battery would run.  Then the last few trips out this fall I saw the run time significantly decrease.  The last time out I barely puttered back to the ramp.  So I figure it's time for a new battery.

My question .... What kind of specs should I be looking for??  Specific battery suggestions???  My MAIN objective is maximize the time I get out of my battery.  I would like to stay under $100 if possible.

In the past I have just taken my old battery into the auto parts store and they picked one out for me.  Now I want to know what to look for.

Thank You

more cold cranking amps the better (cca) and the cold is know to kill batteries also. and i like ac delco batteries i have 4 of them 2 cranking and 2 deep cycle, and i have a 3 bank charger, i charge them after ever use, and leave them charging till the next time i use them

Just look for a "deep cycle" battery, not a starting or "dual purpose" battery. You don't want a battery that list cold cranking amps, (cca) this would be either a starting or dual purpose battery. A deep cycle battery won't list cca on there labels.

Stay with a brand name battery and buy the most amper hours (ah) or reserve capacity (rc) you can afford or house on your vessel. Normally this is a group 31 battery size.

Don't bother with a gel type batteries, just stick with your typical lead acid types.

Another option you have if you want long life is to use 6 volt golf cart batteries. These batteries LOVE to be drained at higher amp draws and will outlast most 12 volts.

here is a good place to learn about batteries.

www.batteryfaq.org