On my boat, I installed a "1/2/both/off battery" switch. I run the motor with the switch on "both", then switch to "1" while fishing, using the trolling motor, sonor, radio, submersible lights, etc. Then switch to "2" to start. After starting, I switch to "both" to charge both batteries while running. That way battery "2" is a dedicated starting battery and I never have to worry about not having a charged battery for engine starts.