You may already have one. Look for 2 yellow wires coming from the stator and going to a rectifier. If you have one I believe it is located on the port side of the motor and very low towards the middle.
Charge rate will be pretty low isn't likely to make up for a days use of fishfinder,live well pump,radio.etc.
Trying to charge a trolling motor battery would be like spitting in the ocean.
