This RV battery maintenance article covers flooded lead acid batteries only.  If you have sealed, gel, AGM or Lithium batteries or don’t know your battery type do not do what is outlined here.  Consult your battery manufacturer’s recommendations for proper maintenance.

Proper RV battery maintenance is crucial for battery longevity and to ensure you’ll have power in your RV when you need it. We had consistent battery problems throughout our time RVing with two different travel trailers.  Our first travel trailer had a single sealed 12v battery setup.  It lasted on average 2 years.  This was running off shore power all summer with occasional trips where the battery was powering the trailer.  No boondocking or extended use on battery only.  This was also with a brand new Progressive Dynamics converter doing the charging and maintaining.

We then upgraded to our new trailer, which also came with a sealed 12V battery.  Unfortunately, the battery didn’t fare any better.  It lasted a year.  Anticipating longer trips and more boondocking we decided to upgrade to two 220 amp hour 6 Volt deep cycle golf cart batteries running in series for 12 volts of power.  These are standard wet cell batteries that you need to add water to.

9 months after installing these batteries and keeping them properly flooded we noticed they drained quickly.  With a light load (interior LED lights on) they would drop to 11.8 V within 3 hours.  This time, instead of upgrading the batteries I decided to upgrade my knowledge.  Here’s what I learned:

So what’s going on here?

The battery chargers in RV converters are lousy.  They will charge your battery (slowly) and it will maintain the battery at a float voltage for as long as you keep it plugged to shore power.  The battery manufacturers will tell you that you can keep your battery healthy in this state indefinitely as long as you maintain proper water levels.  This isn’t necessarily true.  To understand why you have to understand how a battery works.

In the battery, there are lead plates.  These plates are submerged in sulfuric acid.  In a new battery at full charge the lead plates are clean and the sulfuric acid is at its highest concentration.  You measure that concentration as specific gravity (SG) with a hydrometer.  Each battery manufacturer will tell you what the specific gravity at full charge should be.  As the battery discharges, electrons are transferred to the sulfuric acid ions in the water and they bind to the lead plates.  This is sulfation.  When you recharge the battery, the reverse happens.  When recharging, the sulfation is never fully removed from the plates.  As the battery ages, the sulfation layer builds up until at some point it blocks enough of the bare lead plate to prevent the necessary chemical reactions from taking place.  This means electrons no longer flow and you have what we call a “dead battery”.

A typical battery hydrometer. This is used to read the specific gravity of your battery electrolyte. Without it, you are flying blind when trying to diagnose battery issues. At about $5 from any automotive part store there is no reason you shouldn’t have one if your RV uses flooded batteries.

Technically, everything that made the battery good in the first place is still there.  It is just tied up in a way that’s no longer usable.  As it turns out, letting a battery sit for an extended time on a float charger can have similar results.  This was the problem we were having.  Under these conditions, sulfation of the plates can still occur.  Because you are not charging/discharging then you are not cycling the chemicals through the system.  Instead, a thin film of sulfation builds up and gradually thickens over time.  What you’ll see is lowered battery capacity of what they call a  “tired battery”.  Checking the numbers, the specific gravity of the electrolyte will go down.  Even at “full charge” the electrolyte will still test only in the “Fair” range for the battery.

Fortunately, with proper maintenance, this situation can be avoided.  Proper RV battery maintenance will require the proper tools.  Let’s take a look at what we will need.

Proper tools for RV battery maintenance.
1.) Digital Multimeter
2.) Battery Charger
3.) Constant Voltage Power Supply
4.) Hydrometer
5.) Distilled water
6.) Acid resistant thermometer

The digital multimeter is for testing battery voltage.  The hydrometer is for testing the strength, or specific gravity, of the electrolyte.  The distilled water is for refilling the cells to the proper level if needed.  The thermometer is to measure cell temperature during equalization.  The other two items, the battery charger and the constant voltage power supply are the key to battery longevity and need more explanation.

The battery charger and the constant voltage power supply will provide two critical steps in our maintenance procedure.  First is to make sure the batteries are fully charged.  Your converter may not do a good job of this so it is better to use a dedicated battery charger for the task.   The constant voltage power supply will be used to “Equalize” the batteries.  High end battery chargers can have both charging and equalization functions build in, as can many solar charge controllers.  Be extremely careful using that type of setup.  As we will see, equalization involves voltages that can be damaging to some of the more sensitive electronics in your RV such as the refrigerator control boards.  Without proper protection or isolation, equalizing your batteries can cause expensive damage.

What is Equalization?

Equalization is a key step in RV battery maintenance that utilizes controlled overcharging of the battery.  Basically, a higher than normal voltage is applied to the battery.  Each manufacturer will specify the voltage, duration and frequency they recommend for equalizing their batteries.  Generally, the voltage is between 15.5 and 16.1 volts for two 6 volt golf cart batteries in series.  Aside from specific manufacturer recommendations there are two schools of thought on duration.  One is to equalize for 3 hours maximum.  The other is to take hourly specific gravity readings and continue equalization until those readings no longer increase. For frequency, the general rule is between once a month and once a year.  If the specific gravity of the cells drops, or if there is a significant difference (.01 – .02) in SG between cells then it is time to equalize.

Equalization does three things.  It will balance the specific gravity to be equal between the cells.  It also creates vigorous bubbling in the cells.  That bubbling will help dissolve and dislodge the sulfation on the plate faces.  It also helps to mix the electrolyte.  As a battery sits, the electrolyte can stratify – being stronger at the bottom of the battery then at the top.  Equalization cures that issue.

What do you need to Equalize a Battery?

Basically, you need a power supply or charger that can hold the specified voltage constant for as long as you need it.  There are smart chargers with this option built-in.  That will be your safest bet.  Equalization is a dangerous game.  It generates heat and bubbles.  The heat can damage the battery if it gets to excessive.  The bubbles are hydrogen gas, which is explosive.  The next safest option will be a constant voltage DC power supply that puts out enough voltage and current to do the job.  I use a switching power supply capable of making 30 volts and 5 amps.  That is adequate to equalize two 6V batteries in series.  Larger battery sets may need more amp capability.  When equalizing at 15.5 Volts, the current runs about 3.8 amps.

You can also use an old unregulated battery charger if it allows you to set the voltage high enough.  This is your least safe option.  While all of these options will require you to babysit your batteries while equalizing, the old battery charger method absolutely requires it.  These things can take off on you and before you know it your battery is boiled over, boiled dry, overheated or worse of all, on fire.  Do not walk away from your batteries while they are equalizing.

My Procedure for equalizing my batteries:

Again, this is what I do based on my manufacturer’s recommendations:

Frequency: Once a month
Voltage: 15.5V
Duration: 3 hours
Equipment: TekPower TP3005E 30V 5A variable switching power supply in constant voltage mode.
Battery charged full prior to start using a Black and Decker 15Amp Smart Charger.
Specific gravity tested with floating hydrometer

 

Procedure:

  1. Disconnect RV leads from the battery terminals.  This will completely disconnect the RV from the battery during the equalization process.  This is important for 2 reasons.  First, you should not have any loads on the battery while equalizing.  Also, this will isolate all your sensitive circuitry from the higher voltages that equalization requires.
  2. Attach charger and run the charge cycle.  This insures you are starting with fully charged batteries.
  3. Remove filler caps and check electrolyte level.  Adjust with distilled water as needed.
  4. Check Specific Gravity
  5. Attach equalization device
  6. Turn on equalization device and set to proper voltage (15.5 Volts).  Adjust to get into constant voltage mode.  It may take several minutes to get to the proper voltage.
  7. Let the process run for 3 hours, monitoring constantly.  Add water when and if necessary.  Make any adjustments necessary to keep the voltage at 15.5V
  8. Turn off the power supply
  9. Let stand several minutes to allow the gasses to dissipate
  10. Disconnect wires, check SG, add water if necessary and replace caps.

Effectiveness:

Our two six volt batteries have had a specific gravity as low as 1.250, which is in the middle of the “fair” range.  After equalizing, we were able to bring them back up to 1.270 which is considered “new” by the manufacturer.  This shows that with proper RV battery maintenance, your flooded batteries can last longer, perform better and even be recovered from a sleepy state.

 

 

 

 

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