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LIFELINE AGM BATTERIES
Document No. 6-0101 Rev. F Page 11 of 40
3.2 Lifeline
®
versus Gel Batteries
Gel batteries have been commercially available since the early 1970s and are still offered by
some manufacturers. Concorde manufactured gel batteries for many years before developing
the AGM technology and, therefore, is aware of inherent deficiencies associated with gel
batteries.
The gel product employs a highly viscous, semisolid mixture of silica gel and dilute sulfuric acid
in a colloidal suspension as an electrolyte. The electrolyte is difficult to keep homogeneous and
the solid silica can separate from the acid, creating a “flooded” battery. Handling and vibration
exposure are operational factors that can cause the silica and acid mixture to separate as there
is no chemical bond. In high temperature environments, the semisolid electrolyte 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.
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
take twice as long to reach full charge compared to Lifeline® AGM batteries.
The following table provides a side by side comparison of Lifeline® AGM and gel batteries: