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RV Batteries 099

March 8, 2010 by · 3 Comments 


Legions of material have been written on batteries.  You can find more battery information on-line than you would ever have time to read.  When I was teaching, we even had an undergraduate level class that was exclusively about batteries.

Virtually all of our introductory courses at the college were 100, 101, etc.  But, we did have a few remedial courses to help  students who might not be fully prepared  for a 100 level course.  Internally, we often referred to these as 099 level courses.  That is where the “RV Batteries 099” title comes from.

If you have a camping trailer of any type, you have most likely heard the following terms applied to batteries:  lead acid, absorbed glass mat, starting, deep cycle marine/RV,  golf cart, series connected, parallel connected, cold cranking amps, amp hours, reserve capacity and more.

Do you know what all of those terms identify or mean?

Not many people do and thus accept whatever the sales person may give them without question when they buy a battery.  They can only trust that it will be the correct battery for their application.  A fellow professor once commented that there are more people who quote misinformation about batteries than those who quote correct information.  Judging from my encounters, I would have to agree with him.

OK – let’s make it simple for selecting the right battery for a camper without a lot of technical knowledge and facts.

First off, always select a deep cycle battery (note the wing nut terminals on the one pictured above) .  Do NOT use a conventional car starting battery or a combination marine starting/deep cycle battery.

Typical top terminal car starting battery

Deep cycle batteries are made differently – they have thick lead plates.  They are designed to give a consistent amount of power over an extended period of time.  On the other hand, car starting batteries have thin lead plates and are designed to give extremely high power for a short period of time.

So, what type of deep cycle of battery should you buy?   Well my answer is simple - the biggest and heaviest one that you can possibly fit into the required space. The bigger and heavier batteries will have a longer amp hour or reserve minute capacity.  This is a result of additional plates in the battery cells.  Reserve minutes are how long you can expect a battery to provide a continuous 25 amps before it goes dead.  One that provides 125 minutes compared to one with 90 minutes has considerably more capacity and will power your camper for a longer period of time..

The third thing I want you to know about batteries is that temperature has a dramatic effect on their capacity.  If it is a cold 30 degrees outside your battery will not provide its power as long as it will when it is 85 degrees.

The fourth through seventh things are:

Batteries loose capacity as they age.   A four year old conventional lead-acid battery has lost at least 40% of its capacity. Thus a 125 reserve minute battery becomes a  75 reserve minute battery.  Absorbed Glass Mat (AGM) batteries generally have a longer life expectancy if charged and maintained properly.

If the cells have caps that open, check the electrolyte level weekly, especially in hot weather.  Add distilled water to fill them up.  Conventional water may contain minerals that harm the battery or change the pH of the electrolyte.

The charger/converter that came with your camper is probably the best charger you have;  use it,  not a cheap single stage or brute force charger. Years ago camper chargers were pretty inefficient and hard on a battery.

Typical switching converter/charger used in newer campers.

Newer chargers feature at least three charging stages to maintain a battery properly – many add a “Charge Wizard” feature for a complete four stage charging and maintenance program.  Yes, 12 volt camper converter/chargers have changed for the better; its just that too many people are hanging on to old beliefs.

Conventional lead-acid batteries gas out hydrogen.  They can explode if you put a flame over them.  They must be vented to outside air.  NEVER put a conventional vented battery inside a camper living or sleeping area and always keep them away from open flames.  AGM batteries may be used safely indoors since they are completely sealed.  In fact, an AGM battery can be installed sideways or upside down with no ill effects!

Last week I mentioned my son bought a used 2005 Salem.  It had the original group 24 battery box on the front A frame.  The group 24 is one of the smallest camper batteries available and a popular size battery.  We swapped it out for a group 29 – we had to buy a new plastic  battery box but it fit in between the rails just fine.  The battery is typically not included with a new camper from the manufacturer. It must be provided and installed by the dealership.  They often select the smallest and least expensive battery.

Replacing a group 24 battery with a group 27 or even a group 29, which are physically larger, will provide more power over a  longer period of time.   All of these batteries can be connected in parallel  groups of two or more (as long as they match) to add additional capacity.

Two six volt golf cart batteries connected in series will provide improved 12VDC capacity for dry camping.

Some campers elect to use two 6 volt golf cart batteries connected in series to provide the needed 12 volts.  Golf cart batteries are deep cycle and are built to take a lot of vibration.  They make great camper batteries if space allows.

Now – that is really all you need to know about choosing, using and maintaining a camping trailer battery.   Honest!  The other stuff is still interesting and important but is not absolutely necessary for a travel trailer owner to know when buying a new battery.

Many years ago we were camped at Big Meadows on the Skyline drive.  Next to us was a family of four with a camper a lot like the one my son just bought.  Used, clean and expected to be in good condition.  There are no hookups at Big Meadows so we must rely on our batteries for power to run lights, the water pump and furnace..

This was in October when the temperatures in the mountains can drop well below freezing at night.  Our neighbors had been using camper lights for a long time.  I am sure someone took a bath or shower and ran the water pump.  They turned on the furnace to keep the camper warm and went to bed.

For some strange reason I woke up at about 4:00 a.m.  I did not hear the roar of our neighbors furnace that I did at 11:00 p.m. when I took the dog outside.  I knew something was wrong.  After further listening I could hear the motor running on a truck.  I decided to go outside and see what was happening.

The two adult neighbors were in the truck with their children trying to keep warm.  I decided to walk over to the truck.  All the windows were rolled up.  I tapped at the driver window and received no response, I did it again, harder – still no response.   I reached over and gripped the door handle, it opened.  Inside I found four people that appeared to have early stages of carbon monoxide poising.  I managed to get them all awake and out of the truck.  I kept them in fresh air for a while and then took them to our camper.  They made a comfortable nest on the floor and spent the remainder of the night.

The next morning I discovered the battery on their camper was a brand new automotive starting battery – not a deep cycle.  The fan or blower on the furnace draws a significant amount of power from a battery.   The battery quickly became discharged, the blower would not run fast enough to keep the sail switch up and the furnace cut off.

The family was happy to have been rescued by a then active Paramedic and taken to safe quarters.  They also learned a lot about batteries!  The car battery was too small and the wrong type,  The cold weather lowered the power from the battery and the furnace required more battery power than the family expected.  It was a plan for the perfect storm.

There is nothing exceptional about this story other than the happy ending.  All too frequently the wrong choice is made for a replacement battery to be used in a camper.

Be sure to buy a good deep cycle battery, the biggest size you can get to fit in the available space.  Yes, it will cost more.  But, the extra expense is worth it if you do any dry camping!

A great source for additional technical information on RV batteries can be found in  the Woodall’s RV Owner’s Handbook, 4th Edition or from the 34 minute DVD entitled Deep Cycle Batteries in the Woodall’s RV Education 101 Seminar Series.  Both the book and DVD can be found by clicking on the Online Store tab at the top of the Woodall’s home page.

Professor95 – Professor Randy T. Agee

Research RV Accessories for your RV.


3 Responses to “RV Batteries 099”
  1. Brian says:

    Hey Professor,
    I appreciate your technical expertise on these subjects you write about. You mentioned that the converter/chargers in RV’s are getting better, but I can’t tell if mine is a “smart” charger or if it is just like the old ones I have had in the past. We have a 2010 Keystone Laredo 316RL (we really like it!) but I did not recieve much in the way of documentation for the converter/charger system. How do I figure out if it is a good one or if I should upgrade this item?



  2. Dave Mendoza says:

    While having 2 golf cart batteries hooked up in series on my travel trailer, which posts would your solar panel converter be hooked up to? I’m figuring the two end post, one pos. and one neg. going to trailer.
    Thanks, Dave


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