I have a Cabelas AGM 31 size for my starting battery because of all the "toys" connected to it.
HDS8 - HDS7 - LSS-1 - Point-1 - N2K network - 2 live/bait wells - running lights - bilge pump.
Some days I don't run the big motor much so I just want to make sure it will start at the end of the day.
I hate having a dead starting battery on the water.
So far the 2- 27 size trolling motor batteries have worked great for a full day of fishing.

Rick