With the cool chill of winter approaching, you have decided to suspend the use of your boat. Or maybe you are taking a vacation and will be away for a while. But what do you do about your marine battery? How can you keep it charged until the warm breezes of spring blow in, or until you have returned from your vacation?

Is a battery tender the answer? One has worked consistently on your car battery. Let’s take a look and see if a battery tender can be used with a marine battery and, if so, if it will get you the same results. 

What Is A Battery Tender?

As with an automobile battery, a marine battery must be kept in usable condition.

This is especially important when you have a battery that will not be used for a long time. A battery will then consistently lose its charge. If this happens, you may need to recharge the battery when you begin using it again. In some cases, the battery may become discharged completely.

When a battery reaches total discharge, it may not respond to a charge. This would result in you needing to purchase a new battery. Besides the additional expense, you may even need to postpone your boating excursion.

So a battery tender is valuable in maintaining the battery charge and keeping it in usable condition. 

Can You Use A Battery Tender On A Marine Battery?

Battery tenders do work on all batteries, including marine batteries. They work because they do not generate excess heat inside of the battery. Marine batteries last longer when charged with a trickle charger than with a regular charger because excess heat is not generated.

So the question becomes: which trickle chargers are the best to choose?

A favorite is the Noco Genius Gen 3 Waterproof Smart On-Board Charger . Its processor allows it to monitor the power input, making it simple to use.

If charging speed is important, another popular model is the Battery Tender Plus . This charges more quickly than any 3 amp charger.

Minn Kota offers its Onboard Digital Charger . This charger includes Automatic Temperature Compensation. As outside temperature changes, the charger adjusts to prevent battery damage.

If you need to charge more than one battery at a time, consider the Battery Tender 5 Bank . This model can charge five 6-volt batteries simultaneously.

If you need a battery that handles both a cranking battery and a trolling motor, the  will handle the job. The charge will be complete within four hours, even if both batteries were dead when you started charging.

If you want a fast warning that your battery is failing, choose the Tecmate Optimate 6 Ampmatic Battery Saving charger . This charger knows the difference between a discharged and a sulfated battery.

If an emergency pops up and you need the charge done quickly, you need the BMK BlueMickey Smart Battery Charger . It has a mechanism that prevents cell overcharge or discharge.

If you’re concerned about short circuits, choose the Minn Kota MK-105P model . It automatically protects against polarity reverses. You will never have to worry about over or undercharging.

The Dura Volt Marine Solar Panel charger  is simple to install and use. It is made of unbreakable plastic. No glass means no breaking. You can put it on a straight or curved surface.

Finally, one of the most simple models is the Schumacher XCS15 Ship ‘n Shore Charger . It has three simple settings: fast, middle, and low. It instantly adjusts to charge a 6-volt or a 12-volt cell.

So choose according to your needs. Regardless of which of these models you use, it will work with a marine battery.

Now that you know that trickle chargers will charge a marine battery, it is important to know how to use one. As with charging a car battery, you must operate a trickle charger on a marine battery safely.

As the trickle charger slowly adds charge to the battery, it slowly eliminates all batteries’ normal charge depletion when they are not being used. The trickle charger does not merely charge the battery. It also regulates the charge. This way, you avoid overcharging the battery.

The unit itself is basically a box. Inside are the components or “guts” of the charger. Also included are a power cable and two alligator clips. There is usually an amp meter to read the current status of the battery charge and keep track of the charge as it develops.

Before you begin charging, make sure the battery is ready to charge. Keep the charger setup away from splashing water. Be sure the setup is covered to prevent exposure to rain. Since hydrogen gas can be produced during the charge, this helps prevent fires and explosions.

Next, if your marine battery is still in your boat, make sure the ignition is off before connecting the trickle charger. Attach the cables before you plug in the charger. Attach the red connector first, and then attach the negative connector. Plug in the power cable. Do not touch the red and black connectors or you may be shocked.

Turn the switcher on the charger to the on position to begin charging. View the meter to see the current charge amount and to determine how much charge the battery needs. If you do not notice a movement in the measuring needle after a few minutes, your battery may no longer be good.

Remember that different trickle chargers have different capabilities. Some may be used for a few days while others may be used for weeks. Check the charger manual to learn how long your charger will be effective.

How Do You Use A Battery Tender On A Marine Battery?

First, you will need to plug the tender into a standard AC outlet. If you do not wish to remove the battery from the boat, you may need to connect an extension cord to an electrical outlet. The tender normally transfers current at a 12 amp voltage rate.

You will need to consider the weather conditions as you prepare to charge. The colder the weather, the more the battery will likely discharge. So in this situation, plan to connect the battery tender for a longer period.

Battery tenders normally utilize four modes. During the initialization mode, the tender will check to ensure that its components are working. If you do not plan to use the tender for a long time, consider plugging it in any way and allowing it to initialize and draw current. This will help to maintain the tender itself.

Next, the battery tender advances to Bulk mode. In this instance, the tender transfers full charge to the battery. The current transfer is constant, rather than sporadic.

Next, The battery tender advances to Absorption mode. The amps are reduced until the optimum level of voltage for the battery is reached. This prevents overcharge.

Finally, the battery tender changes to Float Maintenance mode. The tender monitors the voltage level and keeps it at full charge. When it has reached Float mode, you may consider removing the battery tender. But if you are still not ready to use the battery, you may consider keeping the connection to keep the battery ready for use.

So let’s take a look at a Youtube video by Captain Leon to see a battery tender in action as it maintains a charge on a marine battery:

When maintaining the battery, the first step is to bring the battery to a warm place or even indoors, if possible. You want to select a battery tender that helps with cranking and deep cycling.The captain explains that total boat care is important while your boat is in storage during the video. Use a cover to protect your boat from harsh weather.

The captain recommends the Interstate Marine AGM battery. This unit includes 1000 marine cranking amps. You will also need a function meter. Ideally, you want to start with the battery resting at 13 volts.

The Battery Tender Plus is his recommended unit. This is not merely a trickle charger. It analyzes how much charge the battery needs. When connecting the unit you are likely to notice a red light, indicating that the battery is low on charge.

As the charge increases, the red light will change to a blinking green light. This tells you that the battery is approaching the desired charge. When the blinking green light turns to solid green, the battery has reached the desired charge level. The captain explains that the battery tender then advances to storage mode.

With the Battery Tender Plus, you can leave the unit in storage mode until the end of the winter or until you are ready to use the battery.

So we have seen that a battery tender will charge a marine battery. A quality unit that is used properly can keep a marine battery going through harsh winters and long boating layoffs. The best tenders not only charge, but also gauge the amount of charge that is necessary. Captain Leon has shown how to keep your boat stored properly. So take good care of your battery and you will hear your engine hum when you are ready to start it up.