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No matter what trolling motor you have, you will need at least one 12V battery to power it.

Today, lead-acid marine batteries such as AGM are still the most popular. However, this is changing fast with falling prices of lithium batteries, which are lighter and offer much better performance.

In this article, you’ll learn about different battery types to help you find the right battery type for your trolling motor.

Let’s get started!

Lead-Acid Batteries

Lead-acid batteries can be further divided into: Flooded, AGM and Gel.

A flooded battery is the most common lead-acid type and is usually the cheapest. However, it is not sealed and has to be regularly maintained. This is done by regularly adding water and using a hydrometer to measure the specific gravity of the battery electrolyte.

An AGM or Absorbent Glass Mat battery is more advanced. It is sealed, won’t leak acid if put on its side, and offers better performance and a longer lifetime than flooded batteries. They can also be stored longer, as they have a lower rate of self-discharge.

Gel batteries are also an evolution of standard flooded lead-acid batteries. The main difference is the electrolyte, which contains silica and gives it a gel-like composition and unique characteristics. Gel batteries can be discharged down to 75% depth of discharge and generally have longer service life than AGM batteries (up to 1000 cycles).

Advantages of Lead-Acid Batteries

Chances are you’ve used a lead-acid battery before, for example bought one for your car.

Lead-acid batteries use a proven, well-known and safe technology.

They are also relatively inexpensive. True, there can be big price differences between AGM, flooded, and gel batteries, but they are still cheaper than comparable lithium batteries.

Plus, most of them can be charged with a regular car battery charger.

Disadvantages of Lead Acid

Lead-acid batteries are heavy. If you ever carried a car battery over a distance, you know what I’m talking about.

Another downside is that you should really discharge them only down to 50% of the rated capacity if you don’t want the battery to age too fast. True, some AGM or Gel batteries can be discharged deeper, but again – their lifetime will shorten.

One big problem with lead-acid batteries is that they suffer from Peukert’s Law. It basically means: the higher the load on the battery, the smaller available capacity. This is especially a problem when you have a smaller battery bank and use your motor frequently at higher speeds or in places where it has to work harder and draws more current.

Although this differs between different types and brands, lead-acid batteries provide only a few hundred discharge/charge cycles. How long the battery will last depends on several factors, such as depth-of-discharge and how well it is maintained. The bottom line is, if you expect a good performance, you will most likely need to replace your batteries after 1-3 seasons, depending on how often you use them.

Lithium Batteries

There are several related types of lithium-ion batteries, but this article discusses only drop-in lithium iron phosphate or LiFePo4 batteries, which are the easiest and safest to use.

Advantages of Lithium Batteries

The first thing you notice about lithium batteries is that they are 2-3 times lighter than lead-acid batteries of similar capacity. This is important, especially if your boat is weight-sensitive or you need to carry your batteries often to recharge them.

They can also be quickly charged and discharged, tolerating high loads and currents without a significant decrease in battery capacity. (the above mentioned Peukert’s Law)

Another big advantage is that lithium batteries have a much longer life expectancy. Good lithium batteries last over 3000 charge/discharge cycles.

Disadvantages

If lithium batteries are lighter, perform better, and last longer, why isn’t everyone using them?

The main reason is that they are still significantly more expensive than lead-acid batteries with a similar capacity.

Also, lithium batteries require a Battery Management System (BMS) to make sure they are properly charged and used to perform as well and as long as promised.

Lastly, they shouldn’t be charged in freezing temperatures. A well-functioning BMS will automatically stop charging the battery when it’s too cold.

Which battery type is the right for you?

It really depends on how much you’re willing to spend up-front. Lead-acid batteries are cheap and if you’re not sure how much battery capacity you will need, go for lead-acid batteries. You can always upgrade to lithium batteries in the future.

Lithium batteries are much more expensive initially but offer much better performance, run time, and they’re much lighter. If you like the best, you should definitely consider them.

Remember to do your research and buy your battery from a source you trust. There is lots of false advertising out there, even scams selling used battery cells as new ones when it comes to batteries. So be careful.

Things to Consider Before Buying New Batteries

Battery Capacity and Run Time

Battery capacity is measured in ampere-hours or Ah and current draw in amperes (amps). If your battery has 100Ah capacity and your motor draws 20 amps of current, you can calculate its run time by dividing 100/20 = 5 hours. However, this is only a theoretical number because depending on the type of battery you use, you will never want to deplete it to 0% of capacity. For example, if you have a standard lead-acid battery, you can significantly extend its life using only 50% of its rated capacity.

The current draw of your motor depends on the speed you set it to and how heavy your boat is. If you use your trolling motor at lower speeds, you will have a significantly lower current draw and much longer run time.

Weather and water conditions will also affect how long your motor will run. It is harder to push a boat against the current, choppy waters, or into the wind, which means higher current draw and shorter run time.

Battery Weight and Dimensions

For most boats, you should consider using larger capacity batteries to maximize your run time. It’s not good for battery longevity to be deeply discharged, and one way to prevent that is to get a battery bank with more than enough Amp-hours.

However, please don’t overdo it, especially when your boat is small. This battery will have to be lifted and carried onto your boat, so before you buy one, check how heavy it is. Also, measure its dimensions, see if it fits in the battery box or wherever you want to stow it.

Stowing Your Battery

On larger boats trolling motor batteries are usually kept in a designated compartment. If your boat doesn’t have one, you can keep batteries in their own battery boxes. This will keep them protected from the elements as well as make them easier to carry.

Choosing the Right Voltage for your Electric Motor

Depending on the voltage of your trolling motor, you will need a different number of 12-volt batteries.

A 12V trolling motor requires just one 12V battery; for 24V and 36V systems, you will need to connect 2 or 3 batteries in series. More batteries of the same size mean more capacity and more range available.

As a rule of thumb, trolling motors with 55 lbs of thrust or less operate on a 12 volts (single battery), those with 68-100 lbs of thrust run on 24 volts (two batteries), and those above 100 lbs of thrust require 36 volts in total (three batteries).

Wiring Your Batteries

If you have a 12 volt trolling motor with just a single battery, the wiring of your system is straightforward:

  1. Make sure the speed of the motor is set to “0”
  2. Connect positive (+) of the motor to positive (+) of the battery
  3. Connect negative (-) of the battery to negative (-) of the motor

And you’re set!

However, let’s take a look at other examples:

Batteries Connected in Series

If you have a 24 volt trolling motor, you will need to connect two 12 Volt batteries in series:

  1. Make sure the speed of the motor is set to “0”
  2. Connect positive (+) of the motor to positive (+) of Battery 1
  3. Connect negative (-) of Battery 1 to positive (+) of Battery 2
  4. Connect negative (-) of Battery 2 to negative (-) of the motor

Batteries Connected in Parallel

For 12 volt systems, an alternative to getting a single large battery is wiring two smaller batteries in parallel. You will then double the capacity while keeping the voltage the same:

  1. Make sure the speed of the motor is set to “0”
  2. Connect positive (+) of Battery 1 to positive (+) of Battery 2
  3. Connect negative (-) of Battery 1 to negative (-) of Battery 2
  4. Connect positive (+) of the motor to positive (+) of Battery 1
  5. Connect negative (-) of the motor to negative (-) of Battery 2

One thing to point out is that batteries wired in parallel should have the same capacity and be roughly the same age.

Circuit Breakers and Fuses

I highly recommend installing a circuit breaker or a fuse between the battery and your trolling motor.

If you keep your battery in a specially designed battery box, it may already be equipped with a fuse. In this case you will need to check if the fuse is the right size for your motor.

Battery Features

Terminals

Battery terminals are frequently overlooked when choosing a battery. There are several different types, with all their pros and cons. Have a closer look at the terminals, and – if possible – read user reviews.

One type of terminal to avoid is the threaded type that accepts bolts. Depending on the material it is made of, you can easily overtighten them and damage the thread. In many cases, this makes a battery unusable.

If your battery has threaded terminals, you should read the battery specifications and find out what torque you should use to tighten them. You will need to get an appropriate torque wrench to do that.

Charging Your Battery Bank

There are two main types of battery chargers out there: smart chargers and manual chargers.

Smart/Automatic battery chargers are also called multi-stage, intelligent chargers. The “smart” thing about them is that they monitor the battery and charge it only when necessary.

This means you can connect your smart charger to the battery and forget about the charging process.

Your battery will be fully charged and properly maintained.

Manual battery chargers are less sophisticated and usually less expensive than smart/automatic chargers.

They don’t monitor the battery and will keep charging it until the charger is disconnected or unplugged.

I always recommend getting a smart charger for your trolling motor batteries. Why? I personally like to leave the charger on without worrying the battery can be overcharged and potentially damaged.

Trolling Motor Battery FAQ

Can I use a car battery instead of deep-cycle/marine battery?

Of course you can, but it doesn’t mean you should. In fact, unless you move only very short distances, you should consider using a deep-cycle/marine battery. A car battery is designed to provide a very high current for a short period of time and begins recharging as soon as the engine starts.

If you use most of your car battery capacity over a short time, it will start deteriorating and not hold its charge very well. Its lifespan will be reduced.

What size battery do I need for a 30 lb thrust trolling motor?

What’s important here is not just the thrust of your motor, but also how heavy your boat is. If this motor is on a lightly-loaded kayak, I recommend a minimum of 50Ah capacity. If it’s anything heavier, for example a jon boat, go with at least 100Ah to be on the safe side.

What is battery equalization and why do you need it?

Equalization is a process of controlled overcharge of a lead-acid battery. It is done to help de-sulfate the battery plates and extend its charge-holding ability and lifetime.