Menu
Cart 0

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 microwave ovens, air conditioners and refrigerators.

What Is a Battery, Really?

Let's briefly define what a battery is in order to help clear up differences between different battery types - a battery is a collection of cells that contain stored electrical power. All batteries have a cathode (the positive element) and an anode (the negative element). They also have some sort of electrolyte, the solution which enables the flow of electrical energy between the positive and negative elements. To be useful, batteries must be affordable, safe, have a long life, fast-charging, and provide a constant source of power. 

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

These four battery types have all been around for some time, with the flooded lead-acid having been in use since about 1860.

Deep-Cycle Battery Types: Pros and Cons

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 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 like flooded batteries, they can be mounted in any orientation, and they 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 

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 some kind of solution of lithium salts that is not water-based. Lithium battery cells can be large or small cylinders, soft plastic pouch cells, or semi-hard 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 1860
  • 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 temeperatures
  • Very low self-discharge, 5% in first 24 hours, then 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 2000-5000 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 complex BMS for protection

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
US Battery US2200 XC2 6V Flooded $130.27 10.25 10.25 11.25 59
US Battery US2000 XC2 6V Flooded $111.43 10.25 10.25 11.25 59
US Battery US12V XC2 12V Flooded $175.23 14 7.1 11.4 86
Fullriver DC224-6 6V AGM $229.95 10.24 7.1 10.7 65.7
Fullriver DC250-6 6V AGM $305.75 12.9 6.8 8.4 76.1
Fullriver DC105-12 12V AGM $258.00 8.3 12.1 6.7 66.6
Fullriver DC115-12 12V AGM $258.00 12.9 6.8 8.4 72.3
Fullriver DC160-12 12V AGM $359.95 19.1 6.7 9.5 100.1
Trojan T-105 Plus Flooded $139.00 10.3 7.1 11.1 62
Trojan J185P-AC Flooded $519.69 15 6.9 14.7 114
Trojan J305E-AC Flooded $208.27 12.2 6.9 14.4 83
Trojan J305P-AC Flooded $259.27 11.7 6.9 14.4 96
RELiON RB100 12V 100Ah Lithium $1,297.56 13 6.7 8.8 30
RELiON RB75 12V 75Ah Lithium $997.56 10.25 6.6 8.6 26
RELiON RB80 12V 80Ah Lithium $1,045.56 12.1 6.8 8.7 28

 

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, charger) 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. Check the specifications for your battery to find the manufacturer's recommended voltages.

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 (this is not required for lithium batteries). Keep your batteries warm, not cold or hot, and they will serve you for a long time. This 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 - ideally 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.