What type of battery should I get to power my trolling motor?

Traditionally the answer is to utilize a deep cycle marine lead acid battery.  These batteries are similar to a car battery but instead of having a high amount of cold cranking amps they have the ability to be run to a lower state of charge without damage.  A better solution is to use a LiFePO4 battery.  These batteries may have a higher initial cost, but will generally last longer than the traditional battery while providing more usable capacity and having a substantially lower weight.