But seriously. It depends on what you plan on doing.
If your stereo is large, and you want to spend a number of hours with tunes and fishing, add a "House" battery... Deep cycle... wire the stereo and other heavy draws to it.
If you spend most of the time riding around, and it is just a head unit, you would likely be fine with just a single battery.
You can never have too much battery, only too little. So the answer to your question is you can get by with just one battery. But buy the largest capacity Dual Purpose (starting/deep cycle) you have room for. For security, buy a jump start unit. The other option is to have a starting battery for the engine and a deep cycle for the high current draw accessories. Connect them with a dual battery switch, ACR (automatic charge relay) or isolator and go boating. In your case, the single battery + jump start unit makes the most economical sense.
Silvertip I am also going with a two battery system similar to this one. I will have a deep cycle marine battery for a fishfinder, trolling motor, gauges and a starting battery for the engine, by using the dual battery switch will I still need to ground both batteries to complete the circuit in that case?
Silvertip I am also going with a two battery system similar to this one. I will have a deep cycle marine battery for a fishfinder, trolling motor, gauges and a starting battery for the engine, by using the dual battery switch will I still need to ground both batteries to complete the circuit in that case?
Yes, always combine the grounds. isolate the positive circuits.
by using an ACR or isolator you protect your trolling motor usage from draining your starting motor while you fish the day away. Use your dual battery switch to turn on and off your starting circuit (i.e. off = motor does not start). Wire the trolling and other items directly to the House battery, use their switches to turn on and off, or add another battery switch.
