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RV Battery 101
Types of RV BatteriesGenerally there are 3 variations in the manufacture of lead acid batteries that are used today. RVs use these deep cycle batteries for their systems like air conditioning, heaters, stereos, and other applications the inverters run.
The three types are referred to as;
1 Flooded (loose liquid electrolyte) lead acid batteries
2 Gel (jelly electrolyte) lead acid batteries
3 AGM (liquid contained by capillary action in a glass matting)
First, let's compare AGM and Flooded Lead Acid BatteriesFlooded-electrolyte lead acid batteries have been around since 1859 and tend to be less expensive than AGM or Gel batteries. However, they have major deficiencies compared to AGM or Gel batteries in RV and Motive applications. For instance, deep cycle flooded lead acid batteries contain antimony in the grid alloy that makes up the plates of the battery. This metal alloy causes a high rate of self discharge and rapid water loss due to gassing reactions. The escape of hydrogen and oxygen from the battery is a nuisance, you must constantly be adding water or the battery dries out. Flooded batteries also carry serious safety hazards;
A. if the gasses are not ventilated properly they can be explosive.
B. if the acid leaks out it is hazardous material.
In flooded batteries, replacing the antimony lead alloy with calcium lead alloy reduces the amount of gassing and water loss, but the cycle life is much lower and they are no longer considered deep cycle batteries.
Electrolyte stratification can occur in all types of flooded batteries. As the battery is discharged and charged, the concentration of acid becomes higher at the bottom of each battery cell and becomes lower at the top of the cell. The acid and water liquids separate like oil and water, naturally creating layers. The low acid concentration reduces capacity at the top of the battery plates, and the high acid concentration accelerates corrosion at the bottom of the battery plates. This acceleration shortens the life of the battery plates, and the battery life. Although stratification can be minimized by raising the charging voltage so that the increased gassing agitates the electrolyte, this will accelerate the water loss and watering frequency. Either way, flooded lead acid batteries require some maintenance.
One other difference between AGM batteries and flooded batteries, flooded batteries can not tolerate freezing temperatures when in the discharged state, whereas AGM batteries are not damaged by freezing temperatures. This means no cracked batteries, ruined concrete garage floors, or worse, antique RVs, cars, and such. AGM Batteries do not corrode the surrounding areas, and won't leak acid.
Second, let's compare AGM (Specifically Lifeline Batteries) and Gel Lead Acid BatteriesGel batteries have been commercially available since the early 1970’s and are still offered by some manufacturers. Concorde (The Lifeline Battery Manufacturing Company) manufactured gel batteries for many years before developing the AGM technology used today. Therefore, Lifeline is aware of inherent deficiencies associated with gel batteries.
The gel battery product employs a highly viscous, semisolid mixture of silica gel and dilute sulfuric acid in a colloidal suspension as an electrolyte (AKA jelly). The electrolyte is difficult to keep homogeneous (AKA evenly mixed) and the solid silica can separate from the acid, creating a "flooded" or "wet" battery. Rough handling or constant vibration can also cause the silica and acid mixture in a GEL battery to separate into liquid and particles, as there is no chemical bond.
In high temperature environments, the semisolid electrolyte GEL develops cracks and voids that reduce contact between the plates and causes the battery to lose capacity. This same effect gradually occurs even at normal room temperatures.
By contrast, AGM batteries employ a glass micro fiber mat separator that holds the liquid electrolyte like a sponge. Shrinkage of the separator does not occur as the battery ages and the electrolyte remains in direct contact with the plates. The electrolyte remains immobilized even when the battery is exposed to severe vibration, so electrolyte spillage or leakage is prevented.
Since it is easier to fill a container with a liquid than a semi-solid, AGM batteries require less space between battery plates. The closer plate spacing gives the AGM battery a lower internal resistance, making it more charge efficient and giving better power performance on discharge, especially at low temperatures.
Gel batteries are also more sensitive to charging voltage. If the charging voltage is not controlled within a very tight range relative to the battery’s temperature, the life of the battery will be adversely affected. For example, one manufacturer of gel batteries claims that if the charging voltage is 0.7V higher than the recommended level, the cycle life will be reduced by 60 percent. The reason for this effect is the limited oxygen recombination capability of gelled batteries. Lifeline® AGM batteries are more forgiving in overcharge conditions and their ability to recombine the hydrogen and oxygen gases back into water is more efficient. With Lifeline® AGM batteries, tests have shown that increasing the charging voltage 1.0V above the recommended charging voltage results in only a 23% reduction in the cycle life.
The charge acceptance of gel batteries is also less than that of Lifeline® AGM batteries. This means it takes longer to recharge gel batteries. As an example, tests have shown that when discharged to 50% of rated capacity (fairly common in a deep cycle applications), gel batteries took twice as long to reach full charge as compared to Lifeline® AGM batteries.
Lifeline Batteries vs Other AGM BatteriesLifeline® AGM batteries have been specifically designed for true deep cycle, long service life capability in adverse temperature and handling conditions. Concorde uses extra thick positive plates, high density paste, thick AGM separator layers encased within a micro porous polyethylene envelope, thick walled containers with epoxy-sealed covers.
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