A deep cycle battery is a lead-acid battery designed to be regularly discharged then recharged again. In a battery, one discharge plus one recharge equals one cycle.
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Deep cycle batteries, may look a lot like car batteries to people who aren’t familiar with them, but in reality, they’re quite different. A deep cycle battery is a lead battery designed to provide sustained power over a long period and run reliably until it is 80% discharged or more, at which point it needs to be recharged. It is important to note that although deep cycle batteries can be discharged up to 80%, most manufacturers recommend not discharging below 45% to extend the life of the battery.
The level of discharge is the “deep cycle” and stands in contrast to other types of batteries that provide only short bursts of energy before they need to be recharged. To be specific, a starter battery discharges only a tiny percentage — usually 2 to 5% —each time it is use.
For the best battery performance and serious off-road adventure enthusiasts, Lithium Batteries are currently the best deep cycle battery option your money can buy. Both AGM and Lithium Deep Cycle Batteries work when a chemical reaction develops a voltage that results in electricity. Deep Cycle Batteries are designed to be ‘cycled’ (discharged and recharged). Hence, while a car battery aims to deliver a burst of energy for a short period, a deep cycle battery gives power at a steady rate for an extended period. In the context of renewable energy, batteries usually mean deep cycle batteries. The two best options for deep cycle battery power are AGM Batteries and Lithium Deep Cycle Batteries are presently the best because of their weight and ability to draw more power from the battery cells.
It is suggested to test your battery’s life when it is fully charged. If you find yourself in a situation where you cannot charge the battery, let it sit for approximately one hour before testing. As a result of charging or discharging, an uneven mixture of acid and water can arise on the surface of the plates. This phenomenon is referred to as a ‘surface charge’, and will need to be removed before the testing begins as it may influence your data. Surface charge can make a bad battery look good and vice versa. To remove the surface charge you can simply leave your fully charged deep cycle battery to sit for at least four hours. Also, ensure your battery is not connected to any appliances or a battery charger as this will influence the data.
Note: if you have multiple batteries connected together, each battery should be disconnected and charged/tested separately.
You can test your deep cycle battery’s charge level in several ways. The most common methods use a multimeter, voltmeter, or watt meter. When you decide to test with a voltmeter, we recommend using a digital meter rather than an analogue meter as it will be more accurate in measuring millivolt differences. For a detailed guide on how to test the voltage of your deep cycle battery, you can have a look at our video .
Once you tested your deep cycle battery’s voltage, you can analyse its state of charge. Simply compare the measured voltage with a state of charge table to discover your battery’s estimated charge level. For example, if your AGM deep cycle battery rates at 12.30V, it’s at a 70% state of charge as shown on our State of Charge graphic. This charge graphic relates to 12V AGM deep cycle batteries, but can also be used as a general guide for other battery types though keep in mind that there may be slight differences in the voltage rating.
Typically, a fully charged deep cycle battery will have a voltage of over 12.8V – 13V. Below are a few common battery problems you can identify by the voltage measurements.
The average lifespan of a deep cycle battery is about 3-6 years. However, the lifespan of a deep cycle battery will vary based on several factors such as the type of battery, how it is used and maintained, and the climate in which it is kept. For example, if you live in a hotter climate, your battery will experience a shorter lifespan than someone living in a cooler climate.
Before you can use your deep cycle battery, you will have to charge it. For the same, you need to keep a few things in mind before charging a deep cycle battery which includes the following:
Sometimes you can tell if your battery is bad by simply taking a good look. There are a few things to inspect:
Broken or loose terminals are dangerous and can cause a short circuit. If a short did occur, there would be some indication of burning or melting. When a battery short circuits, all the power is unloaded in an instant. That produces a lot of heat, and sometimes even causes the battery to explode.
If the battery is still intact, but there is a bulge in the case, this is usually a result of being overcharged. Other signs such as physical openings in the case are often caused by mishandling. Cracks, splits, and holes will not cause a battery to stop working, but for safety reasons the battery should be labeled unsafe to use.
With wet-cell (flooded) batteries, water levels must be maintained. If they are low, usually refilling them with distilled water will help. But, if the cells within the battery have been exposed to air for a long time, it can cause a problem. When the plates within each cell are exposed to oxygen it can rapidly dry the paste that surrounds the lead plates. When the paste has dried it creates a barrier that prevents the chemical reaction within the battery. This can also cause the sulfation that has already occurred to harden leading to a sulfated battery which is the number one cause of early battery failure. We strongly recommend checking the water levels prior to charging a wet cell battery since charging a dry battery will burn it up. If your battery has plenty of fluid in the cells, but the color is dark, or brownish, this is also an indication of a bad battery. Even if one cell is brown, it is rendered useless and therefore the entire battery is, too. Time to replace your battery!
The voltage of a battery is a good way to determine the state of charge. Here’s a handy table with the breakdown:
State of Charge Voltage 100% 12.7 – 13.2 75% 12.4 50% 12.1 25% 11.7 Discharged 0 – 11.6If your battery is:
Sulfation is the natural byproduct when the battery discharges. Naturally, re-charging the battery will reverse the sulfation crystals and turn it back into electrolyte, ready to produce power again. But if a battery sat, uncharged, severely discharged, and/or drained for extended periods of time, the sulfation will increase in size and harden onto the plates. This covers the surface area of the plates, removing the chemicals needed to produce power.
Sulfation decreases the potential to reach a full charge, and it self-discharges the battery quicker than normal. Charging a sulfated battery is like trying to wash your hands while wearing gloves. At this point, charging alone will not restore the battery to a healthy condition. The majority of replacement battery purchases occur when the original battery has reached this point.
Your local automotive shop is more than able to load test your battery, but it’s quite easy to do at home and all you need is a digital voltmeter. For any load test to be accurate, the battery must be fully charged and left to sit 12 hours before load testing the battery. A recently charged battery will hold a residual charge from the charger, so letting the battery sit for 12 hours will release that residual charge and give you a more accurate sense on how the battery will perform under normal circumstances. To the test…
Let’s use a motorcycle battery for an example:
A healthy 12 volt battery should maintain a voltage range from 9.6 – 10.5 volts under the load for a good 30 seconds straight.
For starting batteries we don’t expect you to run the starter for 30 seconds, so if you see the voltage meter drop within the voltage range and it sounded like a good strong start, then you probably just had a discharged battery. However, if under the starting load the voltage drops below 9.6v, then it is most likely time to replace the battery.
For deep cycle application if the battery holds under load for a few seconds then voltage starts to steadily drop this would indicate a problem with the battery. If the voltage instantly drops to 0 volts, that is also a problem. We call this the open cell. On a new battery, this can be a result of manufacturing flaws, but it also may be caused by sulfate crystal buildup.
A common occurrence with open cell batteries is that under the intense heat of the load, one or more of the weld pieces connecting the cells together is coming loose and separating. This will cut the current, and voltage will drop. When the battery cools off, the pieces will touch, barely giving a complete connection. This gives you a false voltage reading. Batteries with open cells may read fully charged in idle, but they fail under a load test every time. Once a battery reaches this point, there is no going back. The best thing to do is recycle the thing.
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Batteries are just batteries, right? They store energy and give it off as needed. Before choosing a battery type, consider what you will be using it for. One battery type will be more suited to your specific purpose than another. Read on to learn more about how these batteries work, what they are used for, and the diffences between lead-acid and lithium deep cycle batteries.
Starter batteries are the sprinters of the battery world. They are designed to put out a lot of power for a short burst. The point usually is to supply the power needed to start something up, like a motor, which then runs on gasoline. They are not designed to discharge much before being recharged and a deep discharge can hurt the battery's lifespan and performance. This is the type of battery you'll find in a car. Once the motor starts, the alternator begins charging the battery back up to full charge. However, this isn't the only application for batteries. Sometimes you need batteries that can continuously supply power for long periods of time, such as to run an electric vehicle.
These are deep cycle batteries — the marathon runners of the battery world. Rather than a short burst of lots of power, they supply a lesser amount of power but for a much longer period of time. Here the batteries are used to run the vehicle instead of gasoline. You may be wondering if both capabilities exist in a single unit. In short, yes, they do, and this is what is known as a dual-purpose battery.
Dual-purpose batteries handle both starting and cycling making them an excellent choice when you are working with a small footprint. They deliver powerful cranking amperage for easy starting, and low amps draw service for reliable auxiliary power. A perfect example of this would be RELiON’s HP series of lithium batteries that are designed to handle getting you started and keeping you running.
As mentioned, deeply discharging a starter battery will hurt its performance. However, deep cycle batteries not only are designed to put out power for a long period of time but also can discharge much more of their stored energy.
The amount you can safely discharge varies from battery to battery. Some batteries can only handle discharging 45% of their energy reserves, whereas others can safely discharge up to 100%.
Just be sure to check the manufacturer's recommendation for your specific battery.
We've already touched on the fact that familiar car batteries are starter batteries. So what are deep cycle batteries used for? In general, for anything that needs continuous power for longer periods of time.
There are also a few types of deep cycle batteries. While they perform the same function, the materials used to build the battery vary. Thus, the different types of deep cycle batteries each have their own pros and cons. Let's look at the main ones here.
This is the oldest type of battery that is still in use. Also called a wet cell, the name comes from the battery having a liquid electrolyte inside, consisting of water and sulfuric acid. If you've ever worked on an older car, you may be familiar with having to open the tabs at the top to add water to the battery on occasion. With deep cycle, flooded lead-acid batteries, adding water is needed more frequently.
Because of the liquid, these batteries must stay upright at all times. They also require good ventilation. Batteries produce hydrogen gas and it must have a way to escape. It is not uncommon for electrolytes to spit out of the vents during charge, leaving acid residue on the battery cover and often even on the battery tray and vehicle chassis.
Overall, flooded batteries require the most maintenance including; adding water, cleaning acid residue from battery covers, terminals, and surroundings. These types of batteries are also quite heavy when considering the ratio of battery weight to the amount of energy they provide. For these reasons and more, their popularity is waning.
Gel and AGM batteries are other types of lead-acid deep cycle batteries, but with a big improvement. They don't have free-flowing liquid electrolytes in them and therefore don’t require any addition of water. They are more expensive though and often don’t last as long as flooded batteries in more demanding applications.
Instead, Gel batteries use a gelled electrolyte and AGM batteries use an electrolyte absorbed in glass matt. If they are used and charged properly, they won’t release any gases, but in the event they overpressure, the safety valve will open and release the buildup. As such, they don't have to remain upright and they virtually eliminate any spillage, cutting down on the corrosion problems common with the flooded variety. They are very popular for use in boats, recreational vehicles, and more.
Lithium-ion batteries are quite possibly the wave of the future when it comes to deep cycle batteries. They require no maintenance, can be discharged more deeply without affecting their lifespan, and charge much faster than other types of batteries.
Because of the higher upfront cost, their popularity has not soared as quickly as you might expect. The fact that they last much longer than lead-acid batteries, can actually make them similar in price or even less expensive over the long run.
And they have many other benefits over their lead-acid predecessors. They are lightweight, they provide their rated capacity at any rate of discharge, they do not get damaged from being left or operated in a partial state of charge, they provide more power throughout the discharge cycle, and more.
Capacity differs greatly between lead-acid and lithium batteries due to their inherently different chemistry. The major difference is their capacity in relation to their rate of discharge. Lithium batteries can provide up to 100% of their rated capacity regardless of their rate of discharge. Lead-acid batteries provide significantly less usable energy with higher rates of discharge. Although both battery types may lose capacity in colder weather the changes in performance are far less drastic with lithium. At 0°C, for example, a lead-acid battery's capacity is reduced by up to 50%, while a lithium iron phosphate battery suffers only a 10% loss at the same temperature.
The lifespan of a deep cycle battery is affected by a few factors. More factors impact the life of a lead-acid battery than lithium. In other words, lead-acid batteries are easier to abuse. Proper maintenance can extend the life, as well as discharge and charge it correctly. Improper watering, over-discharging, over-charging, and under-charging a lead-acid battery regularly can greatly reduce its lifespan.
Lithium batteries don’t require watering, so the issue of improper watering is eliminated. Lithium batteries are not damaged by a partial state of charge, or under-charging, so that issue is also eliminated. Lithium batteries can be damaged if they are severely over-discharge or if they are charged at a high current below freezing temperatures, thereby reducing lifespan.
Heat affects the battery as well. Higher temperatures degrade the battery much quicker.
Because of these factors, plus the fact that different types of batteries have different lifespans, it's hard to state a specific time frame. Check the manufacturer's specifications for your battery to get an idea of the capabilities of your battery.
Now you understand a little about deep cycle batteries. It's obvious why they are important for many different applications. If you still have questions about which battery to choose for your needs, don't hesitate to contact us! We'll be happy to answer your questions and help you decide on the right battery.
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