RV Batteries

 

Battery Types  
Today, there are three distinct types of lead acid batteries manufactured and any one type can be designed and built for either starting or deep cycle applications. These types are flooded acid, gelled acid, and Advanced AGM (Absorbed Glass Mat). There are various quality levels available in each type. Price is dependent upon the perceived quality as well as the product design, processing, and manufacturing costs. This includes the amount of lead, methods of pasting and curing the plates, degree and type of inter-plate insulation, quality of the case, and the sealing method used. Generally, high quality means higher cost.
The oldest types of lead acid batteries are flooded cell types. These have been around for decades. The liquid sulfuric acid solution in these batteries has destroyed more than a few sets of clothes and pieces of RV gear. They generate and vent dangerous explosive gases, acid "mist" during charging, corrode their terminals, often-acid damage surrounding surfaces, and require regular watering. They are the least expensive type and therefore are the choice of many RV owners.
The next types of batteries are gelled acid (Electrolyte) designs. They were introduced to American RVs by Sonnenschein of Germany over 30 years ago and widely touted for their increased efficiency and designed safety features. Their acid is immobilized by adding "fumed" silica to the sulfuric acid solution and then sealing the battery. They internally recombine most of the gases (hydrogen and oxygen) generated during charging and are maintenance free. Gelled electrolyte battery designs are generally quite old and few engineering options are left to improve them. Gel electrolyte is highly viscous and during charge and discharge the gel can develop voids or cracks. These impede acid flow and result in the loss of battery capacity. Also the gelled mixture can liquefy upon charge due to the shearing action of gassing (this property is called thixotropic"). After termination of charge, it can take an hour for the acid to gel again. During this time liquid is moving and the battery can leak if any opening has developed. Last, gel batteries may store hydrogen gas that has not recombined. When overcharging causes a gel battery's vent caps to open, explosive gasses may be vented into the battery compartment. This vented hydrogen has caused a number of "fast failures" or battery explosions.
The latest and most advanced battery technology is Advanced AGM, which was developed to provide increased safety, efficiency, and durability over all existing battery types. In Advanced AGM batteries the acid is absorbed into a very fine glass mat that is never free to slosh around. Secondly, since the plates are kept only "moist" with electrolyte, gas recombination is more efficient. (99% AGM). Thirdly, since the AGM material has an extremely low electrical resistance, the battery delivers much higher power and efficiency than the other two types. Last, Advanced AGM batteries offer exceptional life cycles.
Recombinant gas technology was brought to state-of the-art status at Concorde Battery Corporation, one of the worlds leading suppliers of sealed aviation batteries. The first AGM, "Air Worthy" batteries were delivered to the U.S. Military in 1985 and today are used on the Stealth Bomber, F- 18 fighter jet, and in other demanding military applications. The heavier "fat plate" "Lifelines" were introduced in 1989. Today, "Lifelines" are the most advanced recreational vehicle batteries manufactured in the world. They are subject to the same high standards of design and manufacture as required by FAA and Military Specifications. Additionally, "Lifeline" is the only Advanced AGM product available in standard battery configuration and sizes. They are standard equipment on many U.S. Navy crafts, fine yachts built by Pacific Seacraft, Island Packet, and Hinckley Company to mention three, and quality coaches built by such companies as Vision Coach, Royal Coach and Vantare Coach.

 

A Comparison
Complicated graphs and comparison charts are not necessary to compare the three battery types. Consider:
Safety: Batteries can be dangerous. They store a tremendous amount of energy, create explosive gas during charge and discharge, and contain dangerous chemicals. Some designs and construction techniques are safer than others are. Both Gel and Lifeline Advanced AGM are sealed batteries that use recombinant gas technology. Lifeline Advanced AGM is more efficient in the AGM process and completes its gas recombination near the plates. In fact, they are the only RV batteries to pass the rigid MILITARY-SPECIFICATION for non-gassing even during severe overcharge. A recent Coast Guard Advisory warned all users of Gel recombinant gas batteries to install automatic temperature compensated voltage regulators to prevent explosions associated with their overcharging. Flooded batteries will spew acid, will definitely spill and leak if tipped over, and they generate dangerous and noxious explosive gases. "Lifeline" Advanced AGM batteries are best at protecting both equipment and passengers.
Longevity: All batteries die. The number of cycles it takes to kill them is a function of the type and quality of the battery. When cycled at between 25 to 40 percent depth of discharge (recommended deep cycle use) "Lifeline "Advanced AGM batteries will normally easily outlast the other two types.
Durability: Some battery designs are simply more durable than others are. They are more forgiving in abusive conditions, i.e.; they are less susceptible to vibration and shock damage, over charging, and deeper discharge damage. Gel acid batteries are the most likely to suffer irreversible damage from overcharging. Flooded acid batteries are the most likely to suffer from internal shorting and vibration damage. Lifeline Advanced AGM batteries are more durable and can withstand severe vibration, shocks, and fast charging.
Efficiency: This comparison is critical. Internal resistance of a battery denotes its overall charge/discharge efficiency, its ability to deliver high cranking currents without significant drops in voltage, and is a measure of how well it has been designed and manufactured. Internal resistance in NiCad batteries is approximately 40%, i.e., you need to charge a NiCad 140% of its rated capacity to have it fully charged. For flooded wet batteries, internal resistance can be as high as 26%, which is the charging current lost to gassing, or breaking up of water. Gel acid batteries are better at only approximately 16% internal resistance and require only roughly 116% of rated capacity to be fully charged. Lifeline Advanced AGM has the lowest internal resistance of any battery manufactured only 2 percent. This allows Lifelines to be charged much faster if needed and also to deliver higher power when required. Owners using high output alternators, operating inverter banks, or relying on solar panels can benefit significantly when using Lifeline Advanced AGM batteries with their equipment. "Lifelines" are more efficient!!
Battery Measurements: Most buyers like to make comparisons by using various specifications and measurements. A few common comparison criteria are Cold Cranking Amps or CCA, which is a clear indicator of a battery's ability to start an engine. Reserve Minutes depict a battery's ability to deliver current at steady rates from a fully charged condition down to 10.5 volts and are expressed in minutes, i.e., reserve minutes at 25 amp discharge. Life Cycles are used to measure longevity or how many times a battery can be discharged in its life time at set levels. We compared one of each battery type against various measurements and standards using data published data, as it was available. In our comparison we selected only top quality products; Advanced AGM Lifeline, Sea Gel and Sea Volt. The Group 27 size comparison figures are printed below. An independent comparison of GRP-27 batteries was completed by Cruising World Magazine in June of 1997. Advanced AGM won this comparison.
For more information see www.lifelinebatteries.com
 

Battery Basics
If you look at any battery, you'll notice that it has two terminals. One terminal is marked (+), or positive, while the other is marked (-), or negative. In an AA, C or D cell (normal flashlight batteries), the ends of the battery are the terminals. In a large car battery, there are two heavy lead posts that act as the terminals.

 

Electrons collect on the negative terminal of the battery. If you connect a wire between the negative and positive terminals, the electrons will flow from the negative to the positive terminal as fast as they can (and wear out the battery very quickly -- this also tends to be dangerous, especially with large batteries, so it is not something you want to be doing). Normally, you connect some type of load to the battery using the wire. The load might be something like a light bulb, a motor or an electronic circuit like a radio.

Inside the battery itself, a chemical reaction produces the electrons. The speed of electron production by this chemical reaction (the battery's internal resistance) controls how many electrons can flow between the terminals. Electrons flow from the battery into a wire, and must travel from the negative to the positive terminal for the chemical reaction to take place. That is why a battery can sit on a shelf for a year and still have plenty of power -- unless electrons are flowing from the negative to the positive terminal, the chemical reaction does not take place. Once you connect a wire, the reaction starts.

 

Battery Reactions
Probably the simplest battery you can create is called a zinc/carbon battery. By understanding the chemical reaction going on inside this battery, you can understand how batteries work in general.

Imagine that you have a jar of sulfuric acid (H2SO4). Stick a zinc rod in it, and the acid will immediately start to eat away at the zinc. You will see hydrogen gas bubbles forming on the zinc, and the rod and acid will start to heat up. Here's what is happening:

If you now stick a carbon rod in the acid, the acid does nothing to it. But if you connect a wire between the zinc rod and the carbon rod, two things change: The electrons go to the trouble to move to the carbon rod because they find it easier to combine with hydrogen there. There is a characteristic voltage in the cell of 0.76 volts. Eventually, the zinc rod dissolves completely or the hydrogen ions in the acid get used up and the battery "dies."

In any battery, the same sort of electrochemical reaction occurs so that electrons move from one pole to the other. The actual metals and electrolytes used control the voltage of the battery -- each different reaction has a characteristic voltage. For example, here's what happens in one cell of a car's lead-acid battery:

A lead-acid battery has a nice feature -- the reaction is completely reversible. If you apply current to the battery at the right voltage, lead and lead dioxide form again on the plates so you can reuse the battery over and over. In a zinc-carbon battery, there is no easy way to reverse the reaction because there is no easy way to get hydrogen gas back into the electrolyte.

Modern batteries use a variety of chemicals to power their reactions. Typical battery chemistries include:

 

Also see the following on howstuffworks.com       Use your Back Browser Button to return to cojoweb.com

Introduction to How Batteries Work
Battery Basics
Battery Chemistry
Battery Reactions
Battery Arrangements
Lots More Information!
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Winter storage for batteries, and their state of charge

There is a ritual debate on this topic each year. The concensus seems to be that (1) It's OK to store a battery on a cement floor, but if you stick it on an old piece of plywood, any drips or spills will be easier to clean up, so perhaps the old wives' tale has some value, (2) storing a battery cold in the winter, provided it is fully charged, is an OK thing to do. The rate of discharge is reduced by the cold environment, so less frequent recharging is called for.

Here is an article from Finn Stafsnes, which seems to have some hard data (fs):

The content is taken from a booklet provided by norwegian battery manufacturer (Anker-Sonnak).

I have done some linear interpolation between tabulated values. Therefore minor errors due to non-linear effects may be present. I can only hope that I have not done big errors in my calculations.

State............Spec.gravity.......Freezing.......Spec.gravity of...............@ 25 C, 77 F........point.........@ freez.temp charge..........kilograms/litre.....deg C, F....kilograms/litre

Full (100.75 .50 .25 weak.................1.160..........-17, + 1..........1.189  0  0 If it is impractical to measure the spec. gravity an approximate formula is given based upon voltage measurment:

Spec.gravity (@ 25 C) = ((Voltage of battery)/(no of cells)) - 0.84 (kilogr./lit.)

The voltage should be measured after the battery has been disconnected (left to rest) for at least 6 hours.

A discharged battery will gradually be distroyed if stored in a low state of charge condition due to crystal growth of PbSO4, even if it don't freeze.

Self discharge rate is halved for every 10 deg C (18 F) the storage temperature is reduced.

Conclusion: Keep the battery well charged all the time. If you don't want to recharge during the winter, store the battery cold.

And here is a mini-FAQ written by Alan Yelvington:

The efficiency of batteries varies with time, temperature, and state of charge.

Batteries self-discarge over time. Lead-calcium (die-hard) discharge faster that straight lead-acid. Their advantage is that they typically do not need to have the water replaced.

Temperature will kill a battery over time. If a battery gets too hot, its self-discharge rate goes up. If the battery gets to cold, the reaction that produces electricity gets slowed down and the full capacity cannot be ``harvested.''

The state of charge limits efficiency because of the reactions in the battery. If a battery is left dead for too long (this means you), the internal plates will start to accumulate lead-sulphate on them. This insulates that portion of the plate so that in can no longer contribue to the output of the battery. It takes extra power in to remove the sulphation that cannot be recouped. (EDTA will chemically remove the sulphate....)

A typical battery in good condition will return 90 to 95put into it under these conditions:

DO NOT recharge at a rate of more that one tenth its capacity. eg. A 220 amp-hour battery should not be recharged at more than 22 amps. The excess current will generate waste heat and form lead-sulphite. The lead-sulphite is worse than the sulphate because it cannot be removed.

DO NOT discharge a battery beyond 50 DO NOT over charge the battery. (Lead Sulphite problem again.)

DO NOT discharge the battery faster than one tenth of its capacity. That is, don't draw more than 22 amps from a 220 amp-hour battery. You'll just make waste heat that cannot do work.

DO use the battery and not just leave it dormant all the time. If you must have a battery for infrequent use, NiCd or gelcells are much better and are another story altogether. (ay)

Another reader pointed me towards a nice solar panel charge controller the November, 1993 issue of ``73'' magazine. It's used by a guy with 200 WATTS of solar panels on his roof.


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