How to Pick the Best Trolling Motor Battery for Your Boat

Grabbing the best trolling motor battery shouldn’t feel as unlikely as snapping up a largemouth bass in December.

Still, plenty of anglers find themselves navigating unfamiliar waters when it comes to picking the right battery for a trolling motor. What makes it tricky is all the other marine batteries available, and the label on a trolling motor battery doesn’t usually say “for trolling motors.” Instead, you have a lot of options:

• Do you go with a starting or dual-purpose battery?
• More cranking amps or more amp-hours?
• Do you go with an AGM or a flooded battery?

Trolling motors draw power for hours, but your boat’s main engine only needs an initial burst of power. Plenty of boat owners can match a battery to their primary outboard engine’s cranking requirements.

Picking the right battery for your bow-mounted trolling motor is a whole other kettle of fish.

The Best Battery for Trolling Motors Can Deliver Deep-cycling Power

Deep cycle batteries are the best batteries for trolling motors.

If you’re shopping for a trolling motor battery, the label you’re looking for is deep cycling. Deep cycle batteries are designed to be drained and recharged over and over.

That kind of amp drain will kill most lead-acid batteries, particularly a starting battery.

Think about how a phone battery can drain and recharge a dozen times without dying. Deep cycle batteries can also handle the strain of draining and recharging hundreds of times. That’s what deep cycling means. When a dual-purpose battery like the 34M-AGM marine battery is labeled with “deep cycling power,” that means you can drain and recharge it plenty of times without killing it prematurely.

That said, there are still plenty of deep cycle batteries for your trolling motor.

Which deep cycle trolling motor battery is right for you? It depends on the battery ratings and the battery type.

Which Battery Types Make Great Trolling Motor Batteries?

Battery technology has come a long way in the last several years, and that includes plenty of advances for boat batteries. However, there is no specific trolling motor battery type. Instead, trolling motors rely on deep cycling — and there are three types of lead-acid batteries that work:

• Absorbed glass-mat batteries
• Enhanced flooded batteries
• Deep-cycle flooded batteries

Marine AGM Batteries

Also listed as dual-purpose batteries, marine AGM batteries such as the 31M-AGM can crank engines and drain deeply on a trolling motor. For their weight, they carry more amp-hours than a typical flooded, deep-cycle battery. Meanwhile, they can deliver cranking power if you want one battery for your trolling motor and your primary engine. As a bonus feature, AGM batteries are completely sealed and nonspillable, making them safer to handle in the boat.

Named for the absorbed fiberglass mats that store their power, AGMs are also the same battery type common in start-stop vehicles.

Marine EFB Batteries

Enhanced flooded batteries offer lots of amp-hours because their tightly woven grid packs more lead per battery. EFBs make one of the best trolling motor batteries, especially if you’re looking for a cost-effective way to get AGM-like power. Make sure you select an EFB with the screw-and-bolt and automotive posts like the 24M-EFB marine battery.

Not all EFBs come ready for marine applications. Some EFBs are used in start-stop cars because they have a similar power profile to AGM batteries.

Another thing EFB batteries have in common with AGM batteries: They’re sealed and maintenance-free.

Flooded Deep-cycle Batteries

One of the most common lead-acid batteries for a trolling motor is the flooded, deep-cycle battery. This battery type is designed like most car batteries with lead plates suspended in free-flowing liquid, sealed with vent caps you can use to access the plates inside. They have a distinct chemical difference that allows them to drain deeply without damaging the plates. They’re designed to offer plenty of amp-hours although they do have some cranking capacity.

Choose the Best Trolling Motor Battery Using Two Battery Ratings

To pick the right trolling motor battery, pay attention to these battery ratings when you go shopping:

• Voltage
• Amp hours or reserve capacity

Before you buy a trolling motor battery, you first need to know your trolling motor’s voltage and max amp draw.

Batteries for trolling motors come in 12 volts, but trolling motors themselves come in 12 volts, 24 volts and 36 volts. The voltage of your trolling motor determines how many batteries you need. A 24-volt trolling motor needs two 12-volt batteries, and a 36-volt trolling motor needs three 12-volt batteries.

Also, keep in mind that all the batteries you connect to your trolling motor battery need to be healthy or else the whole set is going to behave like the weakest battery in the bunch. You can test battery voltage to see if your trolling motor battery is ready for the water. A healthy 12-volt battery should have 12.88 volts. If it has less than 12.64 volts, then your battery is at only 75% charge and will probably not last long on the water.

The other specification is related to amps. Max amp draw shows how much power your trolling motor needs when it’s running at full speed. And you need a trolling motor battery that can keep up. Specifically, a trolling motor battery with more amp-hours than your motor’s max amp draw.

Another battery spec you may find on a trolling motor battery is called reserve capacity. Reserve capacity shows how many minutes this battery can give you 25 amps of power. Think of it as the inverse of amp-hours on a battery. If a battery has 60 RC, then it can give your trolling motor 25 amps for one hour. The truth is that most deep cycle batteries can give you much longer than that. The SRM-31 deep cycle battery has a 210 reserve capacity, meaning it can give your trolling motor 25 amps for 210 minutes or three and a half hours.

How Many Amp Hours Should a Trolling Motor Battery Have?

A good rule of thumb is twice your trolling motor battery’s max amp draw. It does depend on how hard you run your trolling motor and how long you need it.

Amp-hour ratings show how many amps your battery will give for one hour. Think of it as a measure of how much time your trolling motor battery will give you on the water. An amp per hour is an amp-hour. A 90 amp-hour battery offers you 90 amps for an hour.

To calculate the run time of a battery with your trolling motor, divide the battery’s amp-hour rating by the trolling motor’s max draw.

A 12-volt, 100 amp-hour battery would last two hours on a trolling motor drawing 50 amps at full power. That said, you probably won’t be pushing your trolling motor at full power for that long. Instead, the same 12-volt, 100 amp-hour battery would last four hours if you kept the trolling motor at half power.

You may want to pick a deep cycle trolling motor battery with more than twice the amp-hours. Batteries with that kind of power often weigh a lot more, which can wind up taxing your motor more than a lighter battery that offers half the power.

How Do You Run a Trolling Motor Off a 12-volt Battery?

To run your trolling motor on a 12-volt battery, you need to connect two or more batteries in a series to get the necessary voltage for your trolling motor. It depends on your motor’s voltage. Connecting in a series is the engineering term for linking batteries positive to negative, which raises their voltage without raising their amperage.

For a 24-volt trolling motor, you need two 12-volt batteries connected in a series. For a 36-volt trolling motor, you’ll need three 12-volt batteries in a series.

Keep in mind that connecting batteries in a series means the performance of the whole pack depends on the weakest battery. If you connect three batteries and just one goes bad, then your trolling motor will stop working.

That’s why we recommend replacing or recharging your whole set of batteries at the same time instead of one at a time.

After all, one weak trolling motor battery can ruin your weekend on the water.