If the motor was originally an electric start it will have the Aux stator (sometimes called a lighting coil or charge stator) and as Jeff noted you will have a pair of yellow wires either just hangin' or connected to an isolator block (just a pair of posts on the side of the block).
If that's the case, then you can add one of Merc's standard square rectifiers (a black square with three posts) to provide "unregulated" power to charge a marine battery (can't use a car battery, the marine battery works as the regulator/capacitor and if you do install a rectifier you must always have a battery attached or you will fry the rectifier and possibly your stator as well).
If the Aux stator is not there it can be installed.
But you should know that this is just a 600 watt unit, so at full throttle it produces 5 amps of charge power - at idle you are not even generating a single amp.
While this is enough to keep a fully charged battery "topped up" if it has a minimal draw (fishfinder or nav lights), it does not provide anywhere near enough power to replace the power sucked from a deep cycle by a trolling motor.
As an example, if you discharged half the amp hours from the average Group 24 battery, you would have to run at full throttle for almost 8 hours to recharge the battery.
You would be far better off running two batteries to supply all your needs for the day and investing in a half decent "on-board" charger and simply plugging in the boat when you get back to the dock...
