Charging a deep cycle battery for a boat. The current controller has connections for battery and another output, I was wondering if I could charge another battery on the other output?
It depends on the type of controller and the voltage on the other battery bank. For example, the Go Power 30 Amp PWM LIthium Bluetooth Controller has room for charging 2 12 volt battery banks. It will charge the first bank completely and then charge the second battery bank.
This will work well as long as you have enough power to fully charge the first bank, if not the second bank will never be sent power.