Gel batteries have been commercially available since the early 1970s and are still offered by some manufacturers today. Concorde manufactured gel batteries for many years before developing the AGM technology and therefore is aware of the 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 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 glass microfiber mat separators that hold the liquid electrolyte like a sponge. Shrinkage of the separator does not occur as the battery ages and electrolyte remains in direct contact with the plates. Electrolyte remains immobilized even when the batteries exposed to severe vibration, so electrolyte spillage or leakage is prevented. Since it is easier to fill a container with a liquid then a semisolid, 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 in 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 batteries temperature, the life of the battery will be adversely affected. For example one manufacture of gel batteries claims that if the charging voltage is .7 V higher than the recommended level, the cycle life will be reduced by 60%. The reason for this effect is the limited oxygen recombination capability of gel batteries. Lifeline AGM batteries are more forgiving and overcharged conditions. Their ability to recombine the hydrogen and oxygen gases back in the water is more efficient. With Lifeline AGM batteries tests have shown that increasing the charging voltage one-volt above the recommended charging voltage results in only a 20% reduction in the life cycles. The charge acceptance of gel batteries is also less than that of Lifeline AGM batteries. This means it takes longer to recharge gel batteries. For an example tests have shown that when discharged to 50% of rate capacity fairly common in a deep cycle application gel batteries took twice as long to reach full charge as compared to lifeline AGM battery. Continue to learn more about batteries and battery technology here on Pete’s Blog.