Here you go azslabber:
StayNCharge by Retrotec
There are a few other products out there but this is one example. Maybe a little more $$ than it's worth for you? Don't know your situation but I would consider adding a second battery for your trolling motor. This way you add capacity to your trolling motor system without worrying about using up valuable power for cranking your motor.
Now you can explore Roosevelt Lake more without worrying about paddling back to Schoolhouse ramp from the Tonto end of the lake...:D
Larry