Battery-powered accessories on a boat often operate on something other than a 12-volt power source. For example, trolling motors often require either 24 or 36 volts. Most readily available batteries do not usually come in those voltages; so you can connect two or more in a series in order to double or triple your voltage while maintaining the same capacity rating (Amp Hours).
A major consideration during this process is battery chemistry, don’t use two different chemistries when connecting in series or parallel. Make sure the voltages are the same, but more importantly the charge rates and capacities are the same to help prolong battery life.
First off, make sure of what you have, you don’t want to feed 36 volts to a 12 volt trolling motor! Once you have determined that you indeed have a 36 volt trolling motor you then need to make sure you have room in the battery compartment for three full size marine batteries. Also, it is wise to go the extra yards and make sure you have either boxes or mounting brackets for all three batteries. You don’t want these power sources flipping all over the hull while you are hitting waves!
Wiring In Series
You will first need to make two jumper wires, approximately 2 feet long. You can obtain the necessary components at any automotive supply store or boat dealer. Once you have these completed you are ready to make the series connection. To make it a little simpler and keep it straight, give the batteries a number designation, such as #1, #2, and #3. It does not matter which number is assigned to which battery as this is done so that the rest of the instructions are easy to understand.
Arrange the power units in the battery compartment of your boat so that their opposite terminals are next to one another. The negative terminal of #1 should be next to the positive terminal of #2, and the negative terminal of the #2 should be next to the positive terminal of #3.
Connect your first jumper wire between the negative terminal of the first battery and the positive terminal of the second battery. Connect your second jumper wire between the negative terminal of the second battery and the positive terminal of the third battery. Fasten the positive lead from the trolling motor to the positive terminal on the first battery. Fasten the negative lead from the trolling motor to the negative terminal on the third battery.
Your series is now complete and you have a full 36 volts of power to your trolling motor. For a 24 volt system, you simply leave out the third battery and connect the negative lead from the trolling motor to the negative terminal of the second battery.
Wiring in Parallel
This method may be useful when you need to double your charge capacity instead of your voltage. In this case, you need your 12 volt charge to endure a longer period of trolling before you discharge completely. This method is called wiring in parallel and is very simple. best trolling motor batteries
You Fasten the positive lead from the trolling motor to the positive terminal on the first battery; and the negative lead from the trolling motor to the negative terminal on the same battery. You then connect a jumper wire from the positive terminal of the first battery to the positive terminal of the second battery; the second jumper wire connects the negative terminal of the first battery to the negative terminal of the second battery. This doubles your capacity of 12 volts to power your trolling motor and twice the run time!