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The Texas Hills

In Minnesota, Bruce Bernhart has been an RV enthusiast since the 1980's


Updated June 30, 2013

The RV Battery Energy System
Cold Weather Tips


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Updated June 3o, 2013

Technical considerations when shopping for a House Battery:

  • Cold cranking amps ("CCA") Available amperage at zero F for 30 seconds to 7.2V
  • Cranking amps ("CA") ia marine environment --same but at 32 degrees F
  • Hot cranking amps ("HCA") same at 80 degrees F
  • None of the above are useful measurements for RVs
  • Reserve capacity (usable minutes at 80 degrees F @ 25 amp draw to 10.5V)
  • Amp-hour capacity: Available amp-hours, at a fixed rate, over a given period of time (e.g. 20 hr rate, 5 hr rate., etc).

Most true deep cycle batteries are at the 20 hour rate. A group 27 battery has about 100 amp hours (5 amps for 20 hours at 80 degrees F). The problem is no one uses exactly 5 amps. If you're pulling 10 amps, you may have a "70 amp hour battery"; if you only draw 2, you may have a 140 amp hour battery. So the amp-hour rating is not really more than a general way to compare like types of batteries.

Comparison Technologies -- How to compare different types of RV batteries.

Efficieny: Measures how much you have to put back versus what you took out. Flooded is 89% efficient; gel cell 95%; AGM is 99%.

Self discharge rate: Flooded 13%; gel cell 3%; AGM 1%.

Cycle life at 50% discharge limit: Flooded 1280; gel cell 400; AGM 1100.

Cycle life at 80% discharge: Flooded 850; gel cell 270; and AGM 550.

Charge set point: Flooded = 14.2-14.6; gel cell13.8-14.0; AGM 14.1-14.4

Float charge: Flooded = 13.2-13.7; Gell cell 13.2; AGM 13.2 -13.4

(Note from the last two measures the relative intolerance of gel cell types. You have several charging sources, such as alternator, shore power/coverter, and solar. It's very difficult to hit the tight tolerances of gel cell type batteries in RVs.)

Presenter highly recommeds AGM batteries for RVs

Input Charge: With flooded battery, charging amperage should not exceed 35% of the amp hours. Thus if you have a 100 amp hour flooded battery, you should not charge it at more than 35 amps. With gel cell, you can recharge at 50%; AGM you can recharge at 100%. Finally note that traditional lead acid batteries require maintenance, while gel cell and AGMs do not.

A note on adding water. Look down cylinder, and fill to the "slit". Always use distilled water. Fill only to the base of the cylinder. Don't fill above that point (water expands when it gets hot); and don't let water go down to where you can see the top of the plates. Reason for not filling above the bottom of the cylinder is that water will expand in volume when hotter, and will spill out the electrolyte, causing corrosion. To clean batteries keep caps on tight, use half teaspoon of baking soda in a cup of water and spray on. It will bubble and fizz -- then just hose it off.

Equalization: This pertains only to flooded lead acid deep cycle batteries. E.g. a Trojan golf cart battery. They will have six caps, representing the six cells within the batteries. Sometimes on recharge one cell will recharge less than the others. 95% of "dead batteries" really means just one dead cell. Equalization is a planned overcharge of the five good cells, while bringing the one bad one up to full voltage. It's better than the option of letting the battery sulphate and ruin that one cell, causing a "dead battery". Suggests equalizing not above 15V, and then adding water immediately afterward.

Best bang for the buck is the Trojan T-105 golf cart batteries -- if you have space for them. They are considerably taller, and won't fit in some compartments. 2 6s in series is better than 2 12V batteries. Longer life, more forgiving, will last twice as long. Cost in range of $65-$85.

Gel batteries cost twice as much, but require very exacting charging regimen. Stay clear of them in RVs.

AGM will cost about 2.5 times that of Trojans. But can be worth it for many RVers.

Dry camping typically takes 50-100 amp hours daily. 2-4 golf cart batteries usually enough for most rigs. 4 needed if you have an inverter.

There are date stamps on all batteries. They want to get rid of old batteries first. If you have different date stamps, you're likely to invite the "different ages" problem, which holds that you need to replace all batteries that are of the same age.

Note: Don't mix battery types, sizes or ages in the same battery bank. Typically if you need to replace on battery, it's time to replace all of them. by Greg Holder, AM Solar, Inc.

Thank you for visiting the Bruce Bernhart RV Websites!

Bruce Bernhart RV Websites

Check out the other Bruce Bernhart RV Websites and Blogs:

Solar power for your RV

The care and feeding of your RV battery

The sport of "geocaching" and RV refrigeration basics

The basics of RV power inversion

RV travel tips and tire care

Advanced discussion on power inversion

Tips on buying a house battery and cold weather maintenance

RV insurance basics

Buying the right generator for your RV and portable power

RV television reception options

Care and maintenance of the RV air conditioner

Top RV destinations

RV long-term supplies and weight considerations

RV insurance- Road protection and bodily injury coverage

RV battery types and winter charging considerations

Deep cycle battery basics


Bruce Bernhart RV Websites

Also, be sure to check out the Bruce Bernhart Mandolin Websites:

Bruce Bernhart mandolin rock tabs

Bruce Bernhart mandolin lessons- common scales

Bruce Bernhart on buying and setting up your new mandolin

Bruce Bernhart mandolin lessons- tuning

Bruce Bernhart mandolin lessons- chord patterns

Bruce Bernhart on mandolin history and basic chord structures

Bruce Bernhart on string and saddle adjustment

Bruce Bernhart more tuning tips and whole/half steps

Bruce Bernhart on more chord patterns

Bruce Bernhart on the mandolin family

Bruce Bernhart on mandolin bluegrass chords and patterns


Bruce Bernhart on temperature considerations

Bruce Bernhart lessson on mandolin flats and sharps


Bruce Bernhart lesson on scales, circle of 5ths and meter


Bruce Bernhart on triads, gears

Bruce Bernhart mandolin chord diagrams

Bruce Bernhart on modern emergence of the mandolin

Bruce Bernhart on simple chords

Bruce Bernhart on whole and half-note steps on the mandolin

Bruce Bernhart mandolin practice excercises

Bruce Bernhart on playing waltzes


Bruce Bernhart on majors, minors and sevenths



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