Wiring a boat battery is not as simple as wiring an automotive system. For example, in some cases 2/0 marine battery cable is a good choice, but not always. Marine applications have different needs and most of them must account for the environment, including weather and water conditions. Here are some common questions and answers about marine batteries.
Q. What is a deep cycle battery?
A. A deep cycle battery is not like a common automotive battery. An automotive battery is designed to use only a portion of the charge before the alternator recharges it. If auto batteries are routinely run down it will greatly shorten their lives.
Many marine applications require a great deal of DC current and batteries can be significantly drained before recharging. A deep cycle battery is designed to have a great deal of its charge drained without affecting the integrity of the battery. In other words, you can run it low time and time again while avoiding problems like you may experience in an automotive battery.
Q. I am running a second battery, how do I size the battery cable?
A. It depends on the load the cables will carry. If it is being used for reserve (and wired in parallel to the present battery) you can usually use the same size cable. For example, if the present battery uses 2/0 marine battery cable, you can probably use the same size for the extra battery—it’s all a matter of ampacity. If you ever find yourself in doubt you should consult with an experienced boat mechanic or electrician to ensure safety.
Q. Can a deep cycle battery be used for starting and general purposes?
A. Yes, deep cycle batteries can handle these tasks. However, if you run two identical batteries, consider using dual-purpose batteries for both.
Q. I am replacing the starting battery for an outboard motor setup. Should I get rid of the old wing nut style connections?
A. It’s a good idea to replace wing nuts with lock washers and hex nuts. You can also use self-locking nuts. Wing nuts can loosen under the intense vibrations caused by outboard motors.
Q. Where is the best place to install another marine battery?
A. Temperature and location are the two most important considerations. Choose the coolest possible place, as high temperatures can lower battery life. Also, select a location closest to the power source so you’ll have the shortest possible cables. For a long length, you may want to go with a larger size like 2/0 marine battery cable. The longer the cable, the more resistance is created due to voltage drop, which can make your cables very hot.
