Demetri Martin, comedian and actor, said, “Batteries are the most dramatic object. Other things stop working, or they break, but batteries…they die.” He left out the part that when they die, life can get a lot more complicated – like being stranded on the water in your boat or having no working electronics. Unless you have a small paddle boat, you have a marine battery or a bank of batteries.

Batteries power everything on the boat – engine, outboard and trolling motors, general electronics, navigation lights, depth finders, fish finders, pumps, stereo system, refrigerator, GPS, and on and on. The marine battery is a workhorse that enables you to enjoy boating, the necessities of life and all the toys you installed on the boat. It is also a specialized energy producer that can quickly start an engine or motor or produce a steady rate of charge to run all the electrical equipment or trolling motor.

Disclaimer: regardless of the advice below, you should have a marine electrician service your boat's batteries at least once a year.

Decisions…Decisions: Choosing a Battery

The right battery and the right battery size is not simple because so many factors must be taken into consideration. - Boat size - Size of the battery box - Number and type of electronics - Number of motors - Electrical demands placed on the battery

The electrical demands include starting the boat and operating the electronics, but it also refers to the way you go boating. Some people like to anchor their boats away from the marina and just relax on the water or offshore. They watch TV, run the heater, turn on the lights, turn on the fish finder and operate other electrical items. The problem is the batteries are being drained unless the engine is running. If this is the way you enjoy boating, you need a deep cycle battery that can be discharged down to approximately 50-80 percent of total capacity (depends on the battery profile) without harming the battery.

Other people like to take their boat out on the water and then troll for fish. You may need a dual cycle battery in that case too. If you only need to start the motor, then you need a starting battery.

Choosing the type of battery is the easier decision. The harder decision is choosing the right size of battery. Batteries are rated for amp hours, but that doesn’t mean you can repeatedly run the battery down based on the rated total capacity. In fact, a best practice is to not discharge the battery more than 50 percent of its rated total capacity because the battery life will be seriously shortened in many cases. So a fully charged 200-amp battery will have a real capacity of 100 amps.

You need to consider the battery capacity (Ah rating), output (MCA, CCA, reserve capacity), and technology (gel, AGM, etc.). There is also a group size which indicates the length, width and height of the battery. For example, a group size 24M is 10 1/4” x 6 13/16” x 9 34”. Knowing the group size is not as important to the purchaser as it once was because the size is usually found on the battery label.

If you have a battery bank or multiple batteries, it’s highly recommended that you install the same type of batteries, e.g. all AGM or all gel. Each type of battery has voltage requirements, so mixing battery types can cause issues like overcharging or under-charging. If you have already mixed batteries, and one dies, it’s the perfect time to increase your investment in batteries and replace all the batteries on your boat.

Avoiding (Most) Battery Surprises with Smart Installation and Maintenance

There’s no doubt about it. One of life’s most frustrating experiences is a dead battery. Following are some basic guidelines for getting the best battery performance and extending the life of your batteries.

• Alternator – Your alternator needs an output that is a minimum of 25-percent of the capacity of all the batteries onboard. An even better goal is 40-percent. This ensures your charging system can deliver the right amperage to charge the batteries. It’s important to monitor your charge voltages to ensure the charging system is always working efficiently. Monitoring can be done manually, or you can install voltage sensing relays. They’re manufactured for specific battery setups, like single battery, single engine with two battery banks, twin outboard engine with three battery banks, etc.
• Avoid new and old – When a battery dies, it’s tempting to just replace the one battery. When you have more than one battery on your boat, mixing old batteries with one or more new ones can harm your new batteries. What usually happens is that the old batteries take charge (pun intended) and bring the new batteries down to their level. Once again, replace all your boat's batteries at the same time to get optimal battery performance.
• Distilled water – Flooded lead acid batteries need water for venting. Use distilled water because it’s free of impurities that could damage the battery’s performance. Always keep the water topped off, even when it’s not in use, for battery performance purposes and to reduce the chances of freezing. The acid in the water prevents the water from freezing.
• Charging – The enclosed non-vented batteries are maintenance free. The flooded lead acid batteries need to be kept charged even when not using them, like during the winter months. Keeping the battery charged, in conjunction with keeping the water topped off, will prevent freezing. A low or discharged charged battery will freeze in cold temperatures. The electrolytes freeze, expand and crack the battery case. A fully discharged battery has a freezing point around 20-degrees Fahrenheit, while a fully charged one can handle up to minus 80-degrees (-800) Fahrenheit. Even if the battery doesn’t freeze, a discharged battery will have a shorter battery life.
• Recharging – Always follow the manufacturer’s recharging guidelines. Each brand and type of battery has specific charging profiles. When the voltage is too high, it can reduce the life of the battery, cause corrosion and lead to faster discharge rates. Also, use the correct battery charger for the type of battery.
• Springing into action – It just has to be said. Before you head out on the water after your boat hasn’t been used for a while, be sure to check all your batteries and the alternator and the electrical system in general. Just because the boat engine cranks the first time doesn’t mean all is well.
• Terminals – All battery terminals are subject to corrosion. It can develop quickly too. It takes very little time to regularly check the terminals for signs of corrosion. A paste made of water and baking soda is the ideal cleaning solution.
• Battery housework – Perform a regular visual inspection of the battery area. The battery compartment should be well-ventilated and clear of debris. If there is a lid on the battery box, keep it on! Even maintenance free batteries should be checked to ensure they are clean and dry. (Mud daubers just love to build their mud nests anywhere they can – sides of batteries, on terminals, etc.)
• Installation - Though it seems like installing a battery is an easy chore, there is such a thing as a poor installation. For example, installing a battery on a battery tray that is too big will allow the battery to slide around. This is where group size can be helpful. Allowing loose cables is another potential problem and can even cause a fire.
• No alternator - Recharge your batteries after every use if you do not have an alternator to keep the batteries charged.
• Hydrometer – If you don’t have a high-quality charging system on your boat, then be sure to use a hydrometer to check each battery cell on a lead-acid battery on a regular basis.

Marine batteries can last for years. The batteries with the shortest life are the lead acid batteries. They may last a minimum of three years with regular use, as long as you follow maintenance tips. The other batteries can last more than five years if kept charged as recommended.

Head’s Up on the Future of Batteries

Some newer style batteries incorporate remarkable technology, like a built-in management system. The system prevents the battery from overcharging. One of the industry trends is fully-electric boats that don’t use fossil fuels and rely on high energy battery storage. This is an emerging technology. In August 2020, Yamaha launched a trial of a new system in Japan that integrates a twin electric boat motor with a next generation steering control system. In Seattle, Zin Boats is also working to demonstrate electric boats are practical. In this case, they are using all carbon fiber construction in some boat models to reduce boat weight and BMW lithium ion batteries that recharge quickly and offer a 100-mile average range.

Over the coming years, there is likely to be a lot of changes coming to the battery industry. Don’t be surprised to discover that one day the flooded and even the gel and AGM batteries become anachronisms.

Take Batteries Seriously!

The battery is a mini-power station that can enable hours of enjoyment or hours of frustration. When buying a battery, it’s crucial to talk to a marine technician to ensure you choose the best option for your boat and boating needs. If you have any doubts about battery installation or suspect an electrical system problem is developing, always hire a marine electrician in your area to service your boat's batteries. This is a case of “better safe than sorry.” Batteries can and do explode, and as one person on the trawler forum said, lead-acid battery explosions are not random accidents. They happen when people are careless or don’t understand how to take care of the battery.

“Know your battery” is some of the best advice you can take. Batteries may die, but they don’t need to die before their time.