6 Things you need to know about deep cycle battery - BRAVA

what is a deep cycle battery

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.

what is the best deep cycle battery

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.

how to test a deep cycle battery

Before testing your deep cycle battery

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.

Testing the voltage of your deep cycle battery

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 .

Analysing the test data

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.

how long does a deep cycle battery last

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.

how to charge deep cycle battery

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:

• To charge a deep cycle battery, you will have to use a multi-stage battery charger that is compatible with your deep cycle battery. These battery chargers charge your batteries in a total of 3 stages which include constant current, constant voltage, and float charge.
• To choose the right multi-stage battery charger for your deep cycle battery, you will have to first ensure that the voltage of your charger matches the voltage of your battery which is generally either 6 volt or 12 volt.
• Now, divide the Ah rating of your battery by 10 to calculate its ideal charger amp rating. While keeping a battery charger for your deep cycle battery, you have to make sure that its ideal charger amp rating is as close as possible to that of your battery.
• Once you have decided upon the right multi-stage battery charger for your deep cycle battery, you have to ensure that you are using it safely as well. And it goes without saying that, you have to keep your battery and charger away from all flames and sparks.
• You should ensure that the charger is turned off whenever you are connecting or disconnecting batteries to it.
• When you are charging batteries, both the batteries and the charger need to be properly vented to prevent overheating.

how to tell if a deep cycle battery is bad

Inspect the Battery

Sometimes you can tell if your battery is bad by simply taking a good look. There are a few things to inspect:

• Broken terminal
• Bulge or bump in the case
• Crack or rupture of the plastic
• Excessive leaking
• Discoloration

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!

Take a Voltage Reading

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 &#; 11.6

If your battery is:

• Reading 0 volts, chances are the battery experienced a short circuit
• Cannot reach higher than 10.5 volts when being charged, then the battery has a dead cell
• Fully charged (according to the battery charger) but the voltage is 12.4 or less, the battery is sulfated

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.

Load Test the Battery

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:

1. Remove the seat and expose the battery in your bike so that you have access to the terminals. Do not disconnect the battery because you will attempt to start the bike.
2. Hold the prongs of your voltmeter to the correct terminals on the battery.
3. Now push the start button and watch what the voltage drops to. It doesn&#;t matter if the bike starts or not, what you&#;re looking for is a voltage reading.

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.

 

For an RV, it's essential to have proper deep-cycle batteries for your battery bank. These batteries will provide the dependable power you need under any conditions, something you'll be grateful for at the end of a long road in the middle of nowhere. What are deep-cycle batteries? These are batteries whose design is optimized for regular deep discharges of power, perhaps even at very rapid rates by power-hungry appliances like induction cooktops, microwave ovens, RV air conditioners and RV refrigerators. Even the most efficient 12-volt RV air conditioners we sell (like the extremely popular Dometic RTX) use 20-50A@12VDC, so we recommend a minimum battery bank size of 400-600 amp-hours (Ah) if you will be running a 12V RV air conditioner in your camper van.

What's New in Deep-Cycle RV Batteries?

Lithium! If you are using power-hungry appliances like the ones listed above, you need to get a lot of power out of your batteries quickly, and then recharge them as quickly as you can. The key advantage of lithium batteries is their ability to accept extremely rapid charge rates - for instance the Relion lithium batteries we sell can be charged at a 1C rate, meaning at 100A for the 12V 100AH battery. That is typically five times faster than most AGM batteries, the next most advanced battery type. Here's a video link that shows the great quality of these batteries - notice the large wire gauges used, the sturdiness of the IP67-rated case, the solidity of the physical pack design, the BMS physically separated from the battery cells, the external heat sink, these are a quality battery.

 

Does everyone need lithium batteries? No - if you are not using any really power-hungry appliances in your RV and thus don't require a very rapid charge rate, you don't need lithium batteries, other types of deep-cycle batteries may work just fine for you.

What is the best type of lithium battery for RV use? Lithium iron phosphate (LiFePO4, a.k.a LFP) is the best type of lithium battery for an RV battery bank: they are not the most energy-dense, but they are not prone to thermal runaway (in fact, they do not catch fire or explode, unlike other lithium types like LCO batteries used in phones and computers), they have long expected lifetimes, and work well as drop-in replacements.

What is the best type of LFP RV battery? This is, of course, a highly-debated question. We are very partial to the Victron Energy LFP RV batteries, and these following two videos explain why: their flexibility (internal or external BMS), their ability to withstand extreme temperatures, their communications capabilities, and their solid build.

The Victron Energy SuperPack lithium batteries include an internal battery management system (BMS), the Victron Energy Smart Lithium batteries use one of the compatible external Victron BMSs (see this BMS Overview sheet).

Victron Lithium Batteries: Part 1

Victron Lithium Batteries: Part 2

 

Why LFP Batteries Are the Best Lithium Chemistry for RV Use

Lithium iron phosphate (LFP) batteries have several advantages over other lithium-ion chemistries, such as lithium cobalt oxide (LCO), nickel manganese cobalt (NMC), and nickel manganese aluminum (NMA). Some of the significant reasons why LFP batteries are superior for use in an RV battery bank include:

The company is the world’s best deep cycle agm batteries supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.

Further reading:
How to compare lithium iron phosphate capacity?

1. LFP batteries have a longer lifespan: One of the biggest advantages of LFP batteries is that they have a longer lifespan than other lithium-ion chemistries. This is because LFP batteries have a lower rate of capacity loss, which means they can be discharged and charged more times without losing capacity. This makes them ideal for use in an RV, where the batteries may be discharged and charged frequently.

2. LFP batteries are safer: LFP batteries are considered to be safer than other lithium-ion chemistries, thanks to their chemical composition. LFP batteries use iron phosphate as the cathode material, which is less flammable and less likely to cause thermal runaway, a dangerous condition where a battery overheats and catches fire. This makes LFP batteries less likely to cause a fire or explosion, which is important in an RV where flammable materials are present.

3. LFP batteries have a higher discharge rate: Another advantage of LFP batteries is that they have a higher discharge rate than other lithium-ion chemistries. This means that LFP batteries can provide more power for a given amount of time, making them ideal for use in applications where high discharge rates are required, such as running an RV's electrical system.

4. LFP batteries are more environmentally friendly: LFP batteries are also more environmentally friendly than other lithium-ion chemistries. This is because they use iron phosphate, which is a more abundant and less toxic material than the cobalt or nickel used in other lithium-ion chemistries. This makes LFP batteries a more sustainable option for powering an RV.

Overall, LFP batteries offer several significant advantages over other lithium-ion chemistries for use in an RV battery bank. They have a longer lifespan, are safer, have a higher discharge rate, and are more environmentally friendly. These advantages make LFP batteries an excellent choice for powering an RV's electrical system.

However, lithium-ion RV batteries are just the latest, most modern version of RV deep-cycle batteries. The following section discusses more traditional types of RV deep-cycle batteries.

Types of Deep-Cycle Batteries

Modern deep-cycle batteries can be classified into four categories:

• Flooded lead-acid
• Gel 
• Absorbed glass mat (AGM)
• Lithium-ion

Let's go into a little more detail about the construction of each type of battery.

Lead-Acid (Flooded)

The flooded lead-acid battery is constructed of lead "plates" or "grids" in a container, called "flooded" because the plates are immersed in a liquid electrolyte. When fully charged, the negative plates are lead-antimony, and the positive plates are lead dioxide, with the electrolyte being concentrated sulfuric acid. As the battery discharges, both types of plates become lead sulfate (undergoing the process described as "sulfation") and the electrolyte loses much of its sulfuric acid and changes to water.

Overcharging/regular charging/undercharging all have effects, as follows:

• Overcharging the battery with a high voltage produces electrolysis, which decomposes the water into its primary components of hydrogen and oxygen gas (this is what is  known as "off-gassing". Overcharging via an equalization charge is sometimes used to restore inadequately-charged flooded lead-acid batteries to a properly-functioning state.
• Regular charging for a lead-acid battery ideally involves multiple stages of charging, usually a bulk charge, an absorption or "topping" charge, and then a float charge to maintain a fully-charged battery. Even during regular charging, there is some off-gassing that happens, which is why lead-acid batteries need regular top-ups with distilled water. If this maintenance isn't performed, electrolyte levels can get low enough to expose the plates, causing irreversible damage.
• On the other side of the charging spectrum, inadequate charging has the temporary effect of not bringing the battery up to a full state-of-charge, and prolonged inadequate charging can also lead to acid stratification, where there is a layer of denser electrolyte and layers of very diluted electrolyte.

Flooded lead-acid batteries have been around for so long because they have many advantages: they have the lowest up-front cost, they are available everywhere, they're suitable for a wide range of uses, and they're a well-known type which everyone is familiar with. But they are not ideal for use in an RV battery bank, and you need to follow the rules - you'll need to install them in an accessible battery box so you can water them regularly, but the battery box needs to be sealed off from the interior of your RV and vented to the outside because of the poisonous gases that can be generated.

Gel (Sealed Lead-Acid)

Gel-cell batteries were created to try and circumvent some of the flooded battery problems. Since the electrolyte is gelled, these batteries are not prone to spills, can be mounted in any orientation, and are sealed so they can be used in areas without much ventilation, since they don't off-gas. Small gel cells are commonly used in power wheelchairs and electric scooters. However, AGM batteries have a much better energy density (the amount of energy stored in a given volume) than gel cells, and gel cells require much slower charging than AGM batteries, two important drawbacks. For these reasons, we don't sell this type of battery.

AGM (Sealed Lead-Acid)

An Absorbed Glass Mat (AGM) battery is another type of sealed lead-acid battery, invented in the s, and very popular for RV use. Unlike a flooded lead-acid battery, all the liquid electrolyte in this battery has been absorbed into the fiberglass mats, which makes for a spill-free battery. Perhaps its best features are its ability to be charged much faster than flooded batteries (up to 5x the charge rate), the ability to deep-cycle (down to depth-of-discharge (DOD) of 80%, producing similar lifecycles as a flooded battery routinely drawn down to 50%), very low self-discharge and not suffering as much from sulfation, and lack of off-gassing under normal conditions. Most AGM batteries do not need or tolerate an equalization charge, with the exception of Lifeline AGM batteries. AGM batteries can be safely located inside your RV, though we still recommend this be in a battery box.

Lithium-Ion 

Lithium-ion batteries are a very different type of battery from lead-acid batteries, whether sealed or flooded. Lithium batteries still have a cathode and anode, but it is lithium ions that move between the anode and cathode, typically in a solution of lithium salts. Lithium battery cells can be large or small cylinders (like the common , and cells), soft plastic pouch cells, or plastic rectangular prismatic cells. Lithium batteries are available in many chemistries, and for RV use, one of the safest, most stable and long-lived types is the lithium iron phosphate battery. Compared to other commonly used lithium battery types (like the lithium cobalt oxide batteries used in cell phones and laptops), lithium iron phosphate has a slightly lower energy density, but is much less prone to thermal runaway, has a very flat discharge curve, and has typically the longest life of any of the lithium chemistries, if well-maintained with good charging practices and moderate temperature conditions. There is no off-gassing whatsoever, and these batteries can be almost completely discharged with no long-term damage. Also, they are half the weight of flooded lead-acid and less than half the volume, and can accept incredibly high charge rates (for example, 100A for a 100Ah battery). 

So how do these different battery types stack up to each other? The table shows some of the major pros and cons of the four types of deep-cycle RV batteries.

 

Type Advantages Disadvantages Flooded

• Low cost.
• Reliable - continuous refinement since
• Robust - tolerant of abuse and overcharging.
• Low internal impedance.
• Can deliver very high currents.
• Indefinite shelf life if stored without electrolyte.
• Can be left on trickle or float charge for prolonged periods.
• Many suppliers worldwide.
• The world&#;s most recycled product.

• Very heavy
• Very bulky
• Typical usable capacity of 30-50%
• Require maintenance - monthly top-off of electrolyte
• Charge efficiency of 70-85%
• High self-discharge, 5% per month
• Can overheat during charging
• Generates poisonous gas when charging
• Cannot do fast charging
• Low cycle life, often 300 to 500 cycles.
• Must be stored fully-charged to avoid damage
• Destroyed by freezing (case bursts, electrolyte spills).

Gel

• Gelled electrolyte (silica added) does not spill as easily as flooded lead-acid
• Gel cells are sealed, so do not off-gas with typical use and charging
• No maintenance
• Low self-discharge, 1-3% per month
• Charge efficiency of 85-90%
• More tolerant of high heat than AGM

• More costly than flooded lead-acid and some AGM
• Cannot tolerate fast charging
• Can be ruined by overcharging
• Require their own specific charging profile, different than AGM, lead-acid or lithium

AGM

• Accept charging at much higher rates than lead-acid or gel
• Usable capacity of 60-80%
• Electrolyte is only in saturated glass mats, so will not spill
• AGM cells are sealed, so do not off-gas with typical use and charging
• No maintenance
• Low self-discharge, 1-3% per month
• Charge efficiency of 95%
• Not affected by freezing

• More costly than flooded lead-acid
• Can be ruined by overcharging

Lithium-Ion

• Usable capacity of 80%-100%
• High energy density
• Extremely high possible charge rates
• No battery memory
• No maintenance
• Very little power loss at low temperatures
• Very low self-discharge, 1-2% per month (lowest if stored partially-charged)
• Very light, very compact (half the weight of lead-acid)
• Charge efficiency of 99%
• Can last - cycles
• Can be stored at low state-of-charge with no damage

• Most expensive up-front cost, may be lowest lifecycle cost of all types
• Some lithium-ion chemistries are thermally unstable, can overheat and catch fire or explode
• Cannot be charged at low temperatures, near freezing or below
• Require BMS for protection, most lithium batteries include an internal BMS

Deep-Cycle RV Batteries Compared

There are an almost infinite number of battery makes and models available for use as deep-cycle RV batteries. The table below compares the deep-cycle RV batteries we sell in the Campervan HQ store - these models and brands have been carefully selected for their quality and longevity.

 

Title Type Price Length (in.) Width (in.) Height (in.) Weight (lbs) Lifeline GPL-27T 12V 100AH AGM $305.00 13.1 6.6 9.25 62 Lifeline GPL-31T 12V 105Ah AGM $304.00 12.9 6.75 9.27 64 Lifeline GPL-4CT 6V 220AH AGM $315.00 10.3 7.1 9.9 66 Lifeline GPL-6CT 6V 300AH AGM $415.00 10.3 7.1 13 90 Lifeline GPL-L16T 6V 400AH AGM $630.00 11.7 7 15.7 119 RELiON RB100 12V 100Ah Lithium (LiFePO4) $1,297.56 13 6.7 8.8 30

 

Deep-Cycle Battery FAQ

Q: Why don't you stock cheaper battery brands?

A: We have purposely chosen quality brands and models that are well-built to endure use as an RV house battery, and which will last years with the proper care. These are not disposable batteries, they are batteries that will continue to serve you well for a long time.

Q: How do I charge these batteries?

A: All of these batteries require a battery charger of some type (like a converter/charger, inverter/charger, solar charge controller, etc.) that is set to the correct charging profile for that type and model of battery. You cannot assume that just because a battery charger has an "AGM" mode that the charger will adequately charge your AGM battery, it must have the voltage setpoints (if adjustable) set to the correct voltages for each type of charging cycle. Currently some of the most popular battery chargers we sell are DC/DC chargers, like the Victron Energy Orion TR chargers. Also most RV inverters (like the very popular Victron Energy MultiPlus 12/ or the newer MultiPlus II 12/) are now inverter/chargers, and have fully-configurable battery settings. When you install your batteries with a battery charger, check the specifications for your battery to find the manufacturer's recommended voltages, and configure the battery charging cycles according to the recommendations for your specific battery model.

Q: Where should the RV battery bank be located?

A: We recommend you locate your RV house battery bank in a sealed battery box in the interior of your camper van, preferably vented to the outside (lithium batteries do not require a sealed or vented box). If you keep your batteries around average room temperature, not cold or hot, they will serve you for a long time. Having an interior battery bank will also minimize the lengths of your wiring runs, which will keep voltage drop low and save you money on materials.

Q: How can I connect batteries together?

A: Batteries can be connected in series or parallel configuration, depending on whether you need to a certain voltage for the battery bank. Most RV battery banks are 12-volt banks, so they have 2 6-volt batteries wired in series, or 2 12-volt batteries wired in parallel. Many 6-volt deep-cycle lead-acid batteries have thicker plates than 12-volt deep-cycle batteries, so they can last longer. Batteries should be physically connected with very thick battery cables sized accordingly, often with 2/0 or 4/0 battery cables.

Q: Can I connect different batteries together?

A: No - any batteries connected together should be of the same type, model and capacity, and the same age. They should also be in one location, and with identically-sized wiring (both in wiring gauge and length) to the charging source. An exception to this is that your camper van engine starter battery can be connected to the house battery bank with a battery isolator, battery combiner or charging relay, so that the house bank can be charged via the alternator or the engine battery charged via solar.

More Information on Deep-Cycle Batteries

Battery University - The most authoritative source we know of for battery information on the Internet.

Wikipedia - Has many thorough articles on battery topics (deep-cycle battery, lead-acid battery, lithium-ion battery, etc).

Battery FAQ - Has up-to-date collected FAQs on many battery topics. 

 

 

 

 

If you want to learn more, please visit our website What is the difference between an AGM battery and other batteries?.