Deep-Cycle RV Battery Buying Guide
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 RTX2000) 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:
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.
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.
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.
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
- Absorbed glass mat (AGM)
Let's go into a little more detail about the construction of each type of battery.
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 1970s, 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 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 18650, 26650 and 32650 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.
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.
|Lifeline GPL-27T 12V 100AH
|Lifeline GPL-31T 12V 105Ah
|Lifeline GPL-4CT 6V 220AH
|Lifeline GPL-6CT 6V 300AH
|Lifeline GPL-L16T 6V 400AH
|RELiON RB100 12V 100Ah
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 12/3000 or the newer MultiPlus II 12/3000) 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.