Using a Deep Cycle Battery For Starting – What You Must Know

There is a lot of confusion among boat owners about deep cycle batteries and how they work. One question involves the use of different types of batteries. People want to know if they really need a cranking or a starter battery or if they could just be using their deep cycle battery when starting up their boat motor. The answer here is somewhat complex. If you have been wondering about your boat motor batteries and how they work, you are in the right spot for the best information.

Using a Deep Cycle Battery For Starting – What You Must Know 1

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Can I use a deep cycle batter to start my boat?

You can probably use your deep-cycle battery to start your boat engine in a pinch. You shouldn’t rely on your deep cycle battery to start your boat engine all of the time because it isn’t designed to do that. Cranking batteries and deep cycle batteries have different purposes and different designs to maximize their respective abilities.

If you want to get in-depth information about these different kinds of batteries; keep reading on as we will break it down even further.

What Is a Deep Cycle Marine Battery?

The deep cycle battery on your boat is designed to be used after the boat has already started up. Once your boat is running, it is similar to your car battery in the sense that it doesn’t need huge bursts of energy. What your boat does need is continuous and reliable power from its battery source.

That is exactly what your deep cycle marine battery is designed to do. The deep cycle battery can run all of your electronics and accessories like your GPS navigation system, fish finders, radio, or things like sonar and other various electronic devices on board.

How is the deep cycle battery designed to do this? It has specific design differences from a cranking battery to perform these jobs. One key area where the deep cycle marine battery is different is its plates.

The plates inside of a deep cycle battery has fewer and thicker plates so that the battery is able to easily provide that consistent power. Deep cycle batteries are designed to be drained and recharged many times repeatedly where as that is not the case with a cranking battery.

When compared to a cranking battery, you will find that a deep cycle battery is much less likely to overheat because their thick plates allow them to withstand the heat over long periods of time.

What is a Cranking Battery?

To actually start your boat, a cranking battery is the one you want. This cranking battery sends power to the engine when the ignition switch is flipped on and that’s why a cranking battery is also known as a marine starting battery.

To get your motor running, you need short and strong bursts of energy from your battery. Those bursts get the whole system moving and don’t really last all that long until your boat is running and should be able to operate on your deep cycle battery.

Using a Deep Cycle Battery For Starting – What You Must Know

As opposed to the deep cycle battery, a cranking battery has a lot of thin plates. They have more plates than a deep cycle battery because they need to have more surface area which will allow these types of marine batteries to send more power to the motor and get the whole system running.

These thin plates are the exact reason why you can’t really use a cranking battery as a “continuous” deep cycle one, because your battery is going to be very prone to overheating.

Why Shouldn’t I Use My Deep Cycle Battery For Starting?

Generally speaking, a deep cycle boat battery simply could fail when the time comes to start a motor. A cranking battery is designed to send short bursts of energy that exceed the output of what a deep cycle one does at any given time.

If you try to start your boat motor with your deep cycle battery, you are risking a pretty big chance that the motor may not start at all.

Even if the boat motor does get started when using a deep cycle battery; you are wearing down the battery and using it for something that it isn’t designed for.

There are theoretical ways that this should work, like if you just had a super strong deep cycle battery.

However, if you do that you are probably just paying more in the long run, and there is a better option for you anyway if you are trying to find one battery for both functions.

Dual Purpose Marine Batteries

A dual purpose battery can be a good solution for some boat owners; however these batteries are not guaranteed to work as well as a separate cranking battery and a separate deep cycle battery.

They combine the use of both batteries into one which seems like it would be convenient, however you should be careful to make sure that your battery performs well because these batteries can have problems at time when they get drained.

If you are out in harsh conditions, a dual purpose battery would also be more prone to overheating due to a compromise of the plate thickness that is found inside of the battery.

If you are not using a battery quite as often, a dual purpose marine battery may be a great option for you, but you just need to find one that offers a lot of quality and doesn’t compromise too much for the performance that you need.

This is just some of the information that you can get about deep cycle batteries. If you are looking for more info, read on!

Sealed vs. Flooded Lead Acid Batteries

Your deep cycle battery may very well be a flooded lead acid battery, also known as a wet cell battery. This basically means that you are able to replace water that is lost in the battery right through the top of the battery.

These batteries tend to be cheaper than gel or AGM cell batteries. They are more work because replacing the water can be annoying, but this is the best value battery that most boaters buy.

If you have a sealed lead sulfuric acid battery, you have bought a model that is essentially maintenance-free. The unit is completely sealed with lead plates so that there is no water loss inside of the battery. You could have an AGM battery or a GEL battery if you have a sealed or dry battery.

How long will my battery last?

One of the reasons that you shouldn’t use your deep cycle battery for starting your vessel is that it will kill the performance of the battery.

Your deep cycle battery isn’t designed for starting a boat, so if you try to use it that way a for longer period of time, you are going to erode its ability over time and pretty much make your battery useless.

How long your battery will last depends a lot on how well your battery is maintained. If you regularly overcharge with too much load or undercharge your battery, it is going to harm your lifespan in a big way.

Batteries are more complex than they seem, so you should always use them in the intended way to get the most out of your purchase.

Your deep cycle battery should last anywhere from 1 to 2 years up to 6 to 8 years on the high end. While it is impossible to guarantee any one battery’s life based on how it will be used, if you are taking good care of your battery and using it appropriately, you should find yourself on the higher end of these ratings.

The best way to take care of your deep cycle battery is to perform regular maintenance on them. That means that they have the appropriate amount of water; and you should try to keep them from discharging too low. Your charger should be monitored so that you aren’t overcharging them either.

If you are going through a season where you aren’t using your batteries at all, you should still be performing somewhat regular maintenance and cleaning and charging them so that they stay in good shape. A maintenance charge can be a great way to make sure that your battery has a long life.

Measuring Battery Performance

You should be familiar with the terms that go along with your battery when discussing performance and the charging factors in a battery.

If you are discussing a battery’s “cycle”, you are referring to one complete discharge and recharge, known as a cycle.

How much a battery has been discharged is often measured in depth of discharge. Basically, this means that if a battery has 50% capacity remaining, the other 50% would be known as its depth of discharge.

If you are using your deep cycle battery regularly, you should know that its lifetime is directly related to that depth of discharge measurement.

If you use your deep cycle battery down to 10% of its capacity, you will not get as long of a lifetime as you would if you were always cycling the battery when it hit 50%.

This is not a reason to be hyper-conservative about your battery life though.

Using your battery for very small doses of power for a short period of time would be impractical and could also harm your battery life as well, so you should honestly try to use your battery in simple and normal ways and you should see some pretty good results.

Should I Equalize My Batteries?

If you have heard of equalizing your battery, you may have heard that this is a great practice and you need to do it. Let’s break it down.

When you equalize a lead acid battery, you are sending a controlled overcharge to the battery to extend its life and make up for lost capacity. This breaks loose a lot of debris that may be stored up on your battery.

If you are completely new to this, it is something you should research pretty thoroughly because you do not want to harm your battery or cause any other damage in the process.

Charging Your Battery

If you are charging your lead acid battery, you should be aware that this charging has 3 stages to it. The stages are bulk, absorption, and float. This why you will hear about 3-stage chargers.

The first stage is the bulk charge. This is when the charger sends current to the cells, basically at the maximum safe voltage that they ca deal with.

That voltage will change depending on the charger and battery; however it is usually between 10 to 15 volts. During the bulk charge state, your battery will charge up for most of its capacity, which is how it gets its name.

The second stage is the absorption charge. This is the stage where the voltage starts to lower as resistance in the battery increases. Usually, your charger is putting out a lot of voltage in this stage, closer to the higher levels that you would have seen during the bulk charge.

The third stage is the float charge. This is what happens after the battery reaches a full charge during the absorption stage. The voltage drops down here a bit to try and prolong the life of the battery.

This is also known as a maintenance charge because it is ensuring that the battery is at full capacity and is ready to go whenever you need it.

Finding a Charger:

When it comes to picking a charger, you will find that there is a big difference between an awesome three stage charger and how it treats your battery and what kind of problems you might get from picking a cheap charger.

The best chargers generally tend to be the ones that have three stages; and these chargers also tend to have a lot of safety features equipped including keeping you safe until a battery is properly connected.

These chargers also tend to be cooled by a fan and can even adjust for things like the temperature while making sure that there are no short circuits.

While you may be a professional and you may be trying to save money, it is still not a great idea to go for a battery charger that doesn’t have any kind of safety features.

The reason for that is that you lose the ability to shut the charger off once you have left the bulk charge stage automatically. When these kinds of things happen, you may be significantly damaging your battery or simply reducing its available life cycle.

Regardless of what battery charger you choose, you should always read the manual and make sure that you are following the manufacturer instructions before you go ahead with any charging.

This is, of course, because there are a lot of different avenues to buy things from these days and you can really buy a product that you think you are familiar with when it actually has a completely different usage than what you thought.

What is an Amp Hour?

If you are trying to measure the capacity of your deep cycle battery, you would do it in amp-hours.

The amp hour is a measure of how much your battery can output when it is fully charged, over time, until it is completely out of power.

Generally speaking, most deep cycle batteries have a rating of 20 hours. That means that you could operate your battery for around 20 hours without it being completely out of power.

However, this is not a simple calculation. It certainly matters how much you are using your battery for and what kind of devices you have connected to it.

For example, if you are trying to use your deep cycle battery for starting your boat engine, you would definitely be affecting the life of your battery if you are even able to get it started that way.

Will the Environment Affect my Battery Life?

It depends on the situation that you are in, however if you are using a lead acid battery you may have different battery life depending on the temperature that you are running your boat in.

Generally speaking, your battery capacity should be better in warmer environments and will be slightly worse in colder temperatures. If it is cold, the battery will have less of a capacity but it may last longer, surprisingly enough.


You should not attempt to use a deep cycle battery for starting your boat, even if it seems like it may be possible.

If you are in a pinch, you could attempt to do this if you are familiar with all of the technology related to your boat.

However, if you are trying to find a battery to use for continuously starting your boat, you should definitely not use a deep cycle battery. It is not equipped for the job and you will end up simply damaging your battery or at least reducing its usefulness in the long run.

You should always try to go by whatever it is that your manufacturer has recommended for your battery.

Using a Deep Cycle Battery For Starting – What You Must Know