Starting, Deep Cycle & Dual Purpose: Breaking Down Your RV Battery Options

Power - by Bryan Veldboom - updated on 9/25/2023

When shopping for RV batteries, it's important to understand that specific batteries are designed to power different applications. Starting batteries do not function in the same way that deep cycle batteries do, and if you use them interchangeably, you could have a real problem on your hands. This article will help you understand the different types of RV batteries and how they should be used.

What are the Three Types of RV Batteries?

Starting Batteries (also known as cranking batteries) - Just like the batteries in your car or truck, RV starting batteries are built to deliver the short, intense burst of power necessary to start your RV's engine. They are not designed to provide long-term power and should not be used as a "house" battery.

Deep Cycle Batteries - A deep cycle battery functions as the "house" battery on an RV. The "house" battery is used to power appliances and other electrical systems when the RV is not connected to shore power. Unlike starting batteries that provide short, intense bursts of power, deep cycle batteries provide ongoing power for longer periods of time.

Dual Purpose Batteries - Dual purpose batteries function as both a starting and deep cycle battery in one. They provide the initial burst of power necessary to start your engine, together with the cycling power required to operate your onboard appliances.

What are the Differences between Flooded, AGM and Lithium RV Batteries?

In addition to different battery types, there are also three different battery chemistries available: flooded (wet cell) lead acid, AGM (short for Absorbed Glass Mat) and lithium iron phosphate (LiFePO4). The chemistry of a battery influences how long it will last, how fast it will recharge and other aspects of performance. Here is a breakdown of the different chemistries.

Flooded Lead Acid Batteries

• Available as a starting, deep cycle or dual purpose battery
• The most affordable of the 3 battery chemistries
• Feature the shortest lifespan of the 3 battery chemistries
• Flooded batteries are not completely sealed and require you to regularly check the electrolyte levels inside and add distilled or deionized water any time the plates are exposed
• Feature a high rate of self-discharge in storage

AGM Batteries

• Available as a starting, deep cycle or dual purpose battery
• Have a higher initial investment than a flooded battery
• Last 2-3 times longer than a flooded battery
• Are completely sealed and require no electrolyte maintenance
• Discharge slower than a flooded battery in storage
• Charge up to 5 times faster than a flooded battery
• Are more resistant to extreme temperatures and vibrations

Lithium Iron Phosphate Batteries

• Available as a deep cycle battery only
• Have a higher initial investment than flooded and AGM batteries
• Last 4-5 times longer than a flooded battery
• Are completely sealed and can be installed in multiple configurations
• Feature the lowest self-discharge of the 3 battery chemistries; rarely need to be charged while in storage
• Can discharge up to 90% before it must be recharged
• Charge 4 times faster than most AGM batteries
• Are more resistant to extreme temperatures and vibrations
• Weigh 55% less than a lead acid battery

How Many Batteries Do I Need In My RV?

Depending on the amount of appliances on your RV, you may require several batteries in order to power it all. If you have a smaller RV with a minimum of battery-reliant appliances onboard, you may be able to rely on a single starting battery. Most RVs, however, will require a starting battery and at least one deep cycle battery, or a dual purpose battery either by itself, or paired with a number of deep cycle batteries.

Calculating the total power (in amp hours) that your appliances require per day will help you determine the size and number of batteries you need. Here is how to do that:

• Start by making a list of all of the appliances on your RV.
• Determine how many amps each application requires in order to run.
• Multiply the number of amps each application requires by the number of hours you plan on using that appliance per day. This will give you the total power consumption of that appliance for the day.
• For example, a laptop uses 5 amps of power. If you plan on using it 3 hours a day, your total daily power consumption for the laptop would be 15 amp-hours of power.
• When the list is complete, add up the daily power consumption of each appliance to tabulate your total power consumption (in amp hours) per day.
• Once you have your total power consumption for the day, select a battery (or batteries) with a high enough amp-hour rating to cover your electrical needs.
• Since lead acid batteries are typically discharged to about 50% of their total capacity, you'll need to divide the battery's listed number of amp hours by two. This will give you the actual usable capacity for the battery. For example, a 100Ah battery will only provide you with 50Ah of usable capacity.
• Lithium iron Phosphate batteries can discharge much lower than lead acid batteries so you don't need to cut their amp hour total. See the manufacturer's recommendations in order to determine how low they can be discharged.

Batteries Plus is Your RV Battery Headquarters

Once you have your batteries picked out, let's talk chargers. While your alternator will charge your RV's starting battery, your deep cycle batteries will require a separate battery charger. Our selection of marine battery chargers can also be used for RV deep cycle batteries.

Still have questions? No problem, our blog has plenty of additional information. Some related topics include "What Does 100Ah Mean on a Battery?" and "How to Maintain Your Boat or RV Battery Over the Winter." Or, stop into your nearest Batteries Plus and ask your questions face-to-face.