Article by Capt. Steve Katz
Battery Basics
Whether it’s the telltale clicking when trying to start your engines or the sudden shutdown of your electronics, electrical problems relating to batteries is a common occurrence.
Most boats use at least one standard marine battery but many use multiple batteries and multiple battery banks. Even a basic 20-foot center console may have two batteries, one for starting the engine and one for operating the accessories. Larger boats may have 8 or more marine batteries arranged in multiple banks. There are few ways you can prevent a sudden battery problem with proper maintenance and equipping your boat with the proper batteries for the task.
It is important to know where your batteries are, where the battery switches are and learn what battery or battery bank is connected to what switch and what loads. (Loads are devices that use electricity, such as engines, electronics, bilge pumps, lights etc).
Boat electrical systems are often separated by function or physical area and often remain separate all the way to the battery switch.
Often a battery switch serves an additional purpose, not just turning off all power from the battery, but it allows you to select where that switch (and loads) gets its power. For example, a popular four position battery switch is labeled “Battery 1”, “Battery 2”, “All” and “Off”.
Knowing what and where “Battery 1” and “Battery 2” are can be very helpful in preventing and fixing a problem on the water. Once you determine the exact features of your battery system, label the batteries and the switches. A label can be as simple as writing on a piece of tape or even writing directly on the switch, wire or adjacent surface. This will help you when it comes time to troubleshoot a problem or even perform routine maintenance.
That common, four position battery switch is often used on a boat with one or two engines and two batteries. Let’s review its proper operation. For simplicity, we will assume we have a single outboard engine and two batteries. Each battery is on its own circuit, up to the point of the battery switch. So if you left the dock with the switch in “Battery 1” position, the engine would start, run and charge only the selected battery and the other battery would just be along for the ride. It would be nice if that other battery was fully charged and ready for use just in case the selected battery went dead, and you could switch over to the good battery and get going again. If you leave the dock with the battery switch in the “Both” or “All” position, and your livewell is left on while you are anchored and the batteries become discharged, both batteries will now be dead, with no back-up available.
So what is the best way to run on one battery while being assured the second battery is ready for use? There are a few ways. The simplest is to keep the battery switch in the all (or both) position while the engine is running, allowing the engine to re-charge both batteries and turning the battery switch to “Battery 1” or “Battery 2” after the engine is off, when anchoring or drift fishing, etc. An automated way of doing this is to use an automatic charging relay (ACR). This device automatically connects the batteries together when the engine is running and charging and separates the batteries when the engine is not charging. This allows you to always have a fully charged back-up battery while running the boat with the battery switch positioned to one battery. Larger boats are more complex in the battery switching and charging systems, but the same principals still apply.
While all boats have different battery systems and configurations, they almost all use a standard size battery, determined by the Battery Council International or BCI. Standardized sizes allow you to choose battery by brand or features and be assured it is the same physical characteristics of the battery you have or need. Popular marine batteries, ascending in physical size, are BCI group 24, group 27, group 31 and group 8D. While many people assume bigger is better, for batteries, there is a lot of variation in performance within the same battery size. While larger batteries are generally more powerful than smaller ones, a high performance, group 24 battery has more capacity than a basic group 27 battery. Make sure you should always read the labels. I often recommend getting the most powerful battery in the size group that fits in your boat, since the incremental cost is minimal compared to the cost of the battery. When referring to “most powerful battery”, if it is a starting battery, you would look for the battery with the most cranking amps. If it is a deep cycle battery, you would look for the battery with the most reserve capacity.
Starting and deep cycle batteries are very different types of batteries. A starting battery supplies lots of power for a very short time and gets recharged immediately. This type of battery is not designed to become discharged often. A deep cycle battery supplies a little bit of power for a long time and is capable of being deeply discharged and recharged regularly. A starting battery should be used to start an engine and that is about it. A starting battery is not designed to run a trolling motor all day or power your electronics while anchored. A deep cycle battery should be used when the battery is regularly discharged and recharged. If the deep cycle battery has enough cranking amps to meet your engine requirements, it can also be used as a starting battery.
In addition to size, there are many types of construction within the same size battery, such as the traditional flooded or wet cell, Absorbed Glass Mat (AGM), Gel cell and lithium ion. This is a topic in itself, though the principals here apply to any of the battery construction chemistry.
Knowing what batteries you have, where they are located and how they are connected will help you enjoy a trouble free season of fishing and boating.
Captain Steve Katz is the owner of Steve’s Marine Service and holds NMEA, AMEI and NMEA2000 certificates along with ABYC Master Technician certification and factory training from many manufacturers.
