12-volt Deep Cycle batteries are the lifeline for RV enjoyment.  Not only do they power the common 12-volt functions like lights, roof vents, and such, but are also essential for powering any appliance running on the LP mode and even the absorption refrigerator on the 120-volt mode as the temperature sensor and monitor panel are powered by the 12-volt batteries!

For the past 50+ years, RVs have mainly been powered by deep cycle, lead acid batteries which have lead plates placed vertically and are covered with a solution of water and sulfuric acid commonly called electrolyte.  In the RV application there is either a 12-volt battery that consists of 6 cells with plates, each producing 2.1 volts per cell.

The other type is a 6-volt batteries connected in series (positive to negative) which creates 12-volts, however two batteries are needed in this application.  There are only 3 cells per battery and each produces 2.1 volts per cell, so each battery produces 6.3 volts or 12.6 volts total just like the single 12-volt battery.  Each cell consists of a positive lead plate covered with lead dioxide and a negative plate made of a specific type of lead with an insulating material placed between the two plates.

These batteries require a specific multistage charging procedure each month and are subject to sulfation if not stored and charged properly.  They “gas” during the bulk stage charge and lose acid which requires periodic inspection.  Most owners do not properly charge and store their lead acid batteries and therefore they have become a hot topic for replacement options.

Gel batteries where introduced in the Mid 70’s and still maintained the lead plates, but had a gel acid instead of the liquid which was designed to be a superior battery with less maintenance.

Then came the AGM or absorbed glass mat battery which was maintenance free and literally had fiberglass mats inside the battery to absorb the acid and could be stored sideways!  Many RVers believe that replacing the lead acid batteries with AGMs will double the power available.  This is not true, rather the AGM batteries require less maintenance and are less prone to sulfation.  This makes them a more powerful battery only after the lead acid batteries develop sulphur between the plates and lose storage capacity!

In 1980 Lithium Ion batteries were introduced, but were not used much until the early 2000’s as the price was out of this world!

12-volt deep cycle batteries are simply storage devices for power, they can not produce or create voltage without receiving a charge from an outside source known as a charger from either a converter, solar panel, or other source.  The size of the plates and amount of electrolyte determine the storage capacity or amp hours (AH) the battery can provide.  These are classified in terms of “Group” ratings such as Group 24, Group 27 etc.  The higher the group rating, the higher the amp hours and therefore the longer the battery can provide power before needing a recharge.  A typical battery rated for 125 AH can provide 10 amps of power for 12.5 hours, or 20 amps of power for 6.25 hours.

Lead Acid Discharge and Sulfation

When a 12-volt source is activated, such as an interior light or roof vent, a chemical reaction between the lead plates and the electrolyte occurs which produces the energy for the light.  This chemical reaction also begins to coat the positive and negative plates with a yellow build up known as lead sulfate which is normal during the discharge process. Lead sulfate continues to coat the plates as the battery discharges to the 10.5 volt stage at which time they are completely covered.

Lead sulfate can be reconditioned back to lead and electrolyte if conditioned or recharged properly and immediately.  If left in a discharged stage the lead sulfate will form hard crystals that can not be converted back to lead and electrolyte and will diminish the storage capacity.

When not in use, all lead acid batteries will discharge, the rate depends on the condition of the battery, temperature, and what parasitic draw is on the battery.  Typically a battery with no sulfation and with no additional draw, will discharge at approximately 4% per week.

A 125 AH battery left in storage without a charger will lose 5 AH per week which means it will lose 80 AH capacity in four months or well over 50% of it’s capacity in just one year!

Proper Recharging

Lead acid batteries require a multistage charge every month which starts with a bulk charge or high voltage (16V) charge which breaks up the Lead Sulfate on the plates and then goes into an equalizing and float charge.  Typical converters and battery chargers are simply a fixed voltage charger that recognizes a low charge (10.5v) and applied a fixed charge of 13.6 volts, which can not reconvert the lead sulfate on the plates.  Plus, the recharge time is very long compared to a multistage charger.

Some larger inverter/chargers do have a multistage charger which will condition the batteries.  Check your system to see if the charger of your inverter has a multistage and conditioning feature.  During the recharge stage, the water is being converted back to hydrogen and oxygen “gases” and can be flammable.  That is why they are contained in a vented compartment.  This is also why lead acid batteries need to have water added periodically as well.  Sealed batteries such as the AGM type contain the gases and keep them with the electrolyte.

There are some alternatives to getting a very expensive inverter/charger such as the Battery Minder from Northern Tool.  This device has had much success in the aviation and golf cart industry and is starting to turn some heads in the RV market.  The Battery Minder uses high impact waves rather than high voltage to condition the batteries which means less gassing and less water loss.

Progressive Dynamics has introduced converters/chargers with a smart charging system called the Charge Wizard which recognized the condition of the battery and adjusts the charge accordingly to provide proper conditioning.  For more on their system visit https://www.progressivedyn.com/rv/power-converters/

Here are some quick tips for better battery maintenance:

1. Use a multistage charger or conditioner
2. Check your fluid level before every trip and add as needed
3. Match the correct size battery with your 12-volt needs.  Don’t expect to dry camp for days on a group 24 battery!
4. Find ways to reduce your need for battery power during dry camping such as
5. Using the campfire to cook and make coffee
6. Replace halogen and incandescent bulbs with LED
7. Use a portable Catalytic Heater vs the RV furnace

About the author:

Dave Solberg: Managing Editor, RV Repair Club

For the last 25 years, Dave has conducted RV maintenance and safety seminars, developed dealer and owner training programs, written RV safety and handyman articles, authored an RV handbook reference guide and logged over 100,000 miles on the road in an RV.

RV Repair Club is your go-to online resource for enthusiasts who want quality RV maintenance, repair, and upgrade information – a community where passionate RVers can come together to gather knowledge and share their experiences.

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