A battery isolator can enable you to charge two different types of batteries (deep cycle and a starter battery) from your motor's alternator without them discharging each other. This is unlike the Series or Parallel connections when you have identical batteries connected together and working in tandem. On many fishing boats with trolling motors a battery charger that can be plugged into 110 volt outlet is already installed. An isolator can be installed if you ever find your self needing an additional deep cycle battery to run added electronics. This allows a charging current to run to both the starter battery and the added deep cycle without current running between the two batteries.
Boat mechanics or parts dealers are able to provide you with an isolator, but equally important would be a diagram of where the alternator wire comes off the main motor. They are also more than willing to help, expecially if you purchase your isolator from them. Here is a diagram of what of a typical installation.
The following picture shows the actual unit installed in a boat. The single post in the middle secures the wire from the alternator. The other two wires run to the starter battery and the deep cycle battery positive post respectively.
Actual Installation On Boat
Boat Wiring is easily understandable. You basically are working with a positive and a negative wire for each electrical accessory. It is also advisable when adding an accessory to be sure to include an in line fuse on the red or positive wire following the manufacturers recommendation. Boats usually will have a built in fuse box or terminal, with a negative terminal built into it. Check on your boat and you may find that this terminal receives its power from the main starter battery. For added accessories it permissable to power them off your starter battery, at least to a point.
You can very quickly run the risk of demanding more power from the starter battery than it was designed to handle. This is especially true if you plan to use these accessories when the main motor is not running and you will not have the advantage of the alternator powering your equipment. This is the time to begin to think about adding an additional deep cycle battery for your accessories. Click on the following link to see a diagram example of wiring accessories to an add on deep cycle battery.