Common Types of RV Batteries
Traditional lead-acid deep cycle RV batteries are usually one of three types: Flooded Wet Cell, Absorbed Glass Mat (AGM), and Gel-cell batteries. Newer lithium-ion (Li-ion) battery technology is starting to infiltrate the market, but these types of batteries are still expensive and impractical.
Flooded Wet Cell Batteries
Flooded wet cell batteries are built with sheet lead plates fully submerged in a conductive electrolyte solution. These RV batteries sometimes need to have the suspension liquid topped off. This liquid can also freeze at low temperatures, or evaporate in a process called electrolysis. This separates the water into hydrogen and oxygen gases, which escape the battery case.
Absorbed Glass Mat Batteries
Absorbed Glass Mat (AGM) batteries use glass fiber mats soaked in the same kind of conductive fluid. These mats fill the space between the electrode plates instead of fully immersing the plates in the fluid. This prevents many of the problems that flooded wet cell batteries have, such as fluid leaking, freezing, or evaporating.
Gel-cell batteries have a gel material that’s a more stable electrolyte fluid. This also prevents any leaking, freezing, and evaporation problems. Both gel-cell and AGM batteries are called “maintenance-free” batteries because they do not need regular refilling for the suspension liquid.
How to Prevent and Remove Sulfation
An important part of the maintenance of lead-acid batteries is to keep them free of corrosion, or more accurately, sulfation. Storing your batteries when it’s not fully charged will cause sulfation, which is the growth of sulfur crystals on the lead plates or battery terminals. Sulfation is a leading cause of battery failure.
The best way to prevent sulfation is by keeping your batteries fully charged when you’re storing it during the off-season. When sitting in storage for long periods, they will self-discharge. You might leave your batteries disconnected for several months and find its terminals or plates covered with sulfur corrosion.
To make sure they stay charged and healthy, you should check the charge once every month with a multimeter. If the voltage drops significantly, then use a battery charger to charge.
If you only have minor sulfation inside the cell, slowly reconditioning it may clear the sulfation up. Follow these steps to safely recharge it and reverse the sulfation:
- Remove the plastic cover with a flat-head screwdriver.
- Check the fluid level inside. The fluid should rest between the high and low fill markers.
- Carefully refill each cell with distilled water until the fluid level is restored.
- Connect the alligator clamps from your external battery charger to the terminals. Connect the red terminal first, then the black terminal.
- Set the charger to its lowest setting, and then plug it into an outlet.
- Leave your lead acid battery charging for 36 hours. Check after the first 12 hours to make sure the fluid is forming small bubbles. This indicates de-sulfation.
- After 36 hours, check again. If there are no bubbles at this point, the battery may be dead.
Corrosion on the terminals is a different matter. This kind of sulfation can be removed with a wire brush and a solution of baking soda in distilled water. Mix a quarter cup of baking soda with one and a half cups of distilled water, and apply this to the terminals. Let it soak for about five minutes, then use a stiff wire brush to scrub the terminals.
Maintaining Flooded Wet Cell Batteries
The two most important things to maintain flooded wet cell batteries are (1) Maintaining fluid level and (2) Preventing freezing.
If your fluid leaks or evaporates, you can refill the unit with distilled water. Keep your battery stored in a warm, dry location to prevent the fluid from freezing.
Another important maintenance procedure is called equalizing. Flooded cell batteries can develop acid stratification, where the acid becomes more concentrated at the bottom than at the top. Equalizing your battery means overcharging it with a high voltage charger which should restore the chemical balance inside the fluid.
Maintaining Battery Housing
Unfortunately, if the housing becomes cracked, or otherwise compromised, this means you will have to replace the lead acid battery. There’s no recommended way to repair the housing of house batteries.
Keeping your RV batteries clean can protect the housing. You can clean the housing with the same baking soda solution that you used on the terminals. Don’t allow other chemicals or heated items to come in contact with the battery case. Also, keep RV batteries out of direct sunlight and UV rays, which can degrade the plastic of the housing.
Maintenance on Battery Connections
If you are frequently removing your RV batteries and reinstalling it in your motorhome, it’s not uncommon for the connections to become loose or worn out. Always use the proper tools when adjusting the connections to the battery (exact fitting wrenches are better than pliers). Tight terminal connections are less prone to excessive sulfation.
Discharging and Recharging RV Batteries
How Batteries Are Charged
Deep cycle 12-volt batteries will only charge once they are connected to a power supply with a voltage supply greater than 12 volts. Typically 120 or 240 volts. This will generate a current that passes through the battery, causing the internal lead plates to polarize and store a charge. The greater the current, the faster the charging will occur.
State of Charge
A fully charged lead-acid battery will have a voltage of 12.7 volts. Gradually over time the voltage decreases as the energy in the battery declines, either due to powering appliances or just due to the passage of time.
Many problems arise from users who discharged their RV batteries too far. You should never discharge your battery further than 50 percent, which will typically be reflected by a voltage of ~12.2 volts.
To ensure long battery life, charging your batteries should be done as often as necessary to keep the state of charge between 12.2 -12.7 volts. This can be done using a generator, solar panels, by the camper’s engine via the alternator (if you’re driving) or by connecting to shore power (either by using battery chargers or a converter). Charging your house batteries should be done in stages to help maintain lifespan:
- Bulk Charge (or bulk stage recharging): Charge to 90 percent.
- Absorption charge: Top off the remaining 10 percent.
- Float charge (or maintenance charge): Use a trickle charger to keep the battery at full charge.
Testing and Inspecting RV Batteries
Regardless of which type of RV batteries you use, you should inspect your battery once a month.
Your inspection should start with the housing – see if there is any corrosion, cracks, or noticeable leaks.
Next, open the housing to check the fluid levels inside. The inside should have markings to indicate the minimum and maximum fluid levels. If the fluid is low, refill the battery with distilled water.
Finally, check the specific gravity of the fluid using a refractometer or hydrometer. This specific gravity reading can be compared against charts to check the charge.
Alternatively, you can close up the battery again and check the charge using a multimeter.
How to Use a Multimeter
Set your voltmeter to DC voltage, or your multimeter to 20 volts (depending on which type of meter you have).
Touch the red lead to the positive terminal on your battery. Then touch the black lead of the meter to the negative terminal.
The screen should read between 12.5 and 12.7 volts. If the reading is high, you should discharge the battery by using your RV appliances. If the reading is low, then charge the battery as necessary.
How to Use a Refractometer or Hydrometer
When using a refractometer or hydrometer, you will be measuring the specific gravity of the battery suspension fluid. Because this fluid is hazardous, you should always start this procedure by wearing gloves, closed-toe shoes, and goggles for personal safety.
Using a Refractometer
- Carefully open the vent caps on the casing.
- Using a pipette, draw a few drops of sulfuric acid from inside the battery.
- Place a few drops onto the testing plate surface of your refractometer.
- Close the cover of the refractometer.
- Keeping the refractometer fairly level, hold it up to your eye to take a reading of the specific gravity. This must be done in a well-lit area. You will see a shadow line that delineates a scale inside the refractometer.
- Repeat this procedure for every battery cell.
Using a Hydrometer
- Carefully open the vent caps on the casing.
- Insert the hydrometer and suck some fluid into the chamber using the squeeze bulb. Flush the chamber with this fluid a few times.
- Draw a full sample into the chamber.
- Hold the hydrometer vertically at eye level and note the specific gravity reading.
- Repeat this procedure for every cell in the battery.
In both procedures, the specific gravity should read between 1.255 and 1.275 for a fully charged battery. This may need to be adjusted for ambient temperature. Also, this is a good time to inspect the fluid for discoloration. Brown or gray cloudiness in the fluid indicates that the battery is nearing the end of its life.
Storing Your RV Battery
Since you may not be using your RV all year, an important part of lead-acid battery maintenance is your storage procedure.
Your RV battery storage area should be:
- Off the ground.
- In a cardboard tray.
When putting your RV batteries away in storage, always start the process by ensuring that they are fully charged.
During extended storage, you should schedule check-ups on your RV battery for once a month. For these check-ups, you should open the casing to check the water levels. You should also use your multimeter to check the battery voltage, and possibly top-up the battery charge if it’s dropping.
If you have a trickle-charger, this is an excellent accessory for storage. A trickle-charger provides a slow continuous float charge, that will keep your batteries charged without ever overcharging them.
It’s important for all RV owners to understand how to conduct proper maintenance on your recreational vehicle batteries in a safe manner.
First of all, make sure you disconnect your RV from its power source and that the battery disconnect switch is turned off before working on the battery. Your 12-volt battery cannot electrocute you, but your 120-volt outlets certainly can.
Whenever you are working on your RV battery, you should be wearing gloves. While there is little risk of electrocution, the battery contains acid, which can burn your skin on contact. You should also wear closed-toe shoes to protect your feet in case of splashing.
Goggles are also recommended safety items when working with lead-acid batteries. The acid is particularly dangerous if it gets in your eyes, and may lead to blindness.
Whether you’re a newbie or an old hand we hope that this article has taught all RV owners something about the importance of maintaining your RVs 12-volt battery electrical system. If you found this RV article useful, please feel free to share it with other campers, friends, and family members. If you have any more advice or questions, please add them in the comment section!