A buddy of mine turned me on to AGM batteries. I beleive he is a member on this forum, so he may chime in with more info. I just purchased a pair of rebuilt group 31 batteries for my trolling motor for the price of one Optima battery. You may want to search if there is a business that deals in nothing but batteries for your area.
What is a AGM or Absorbed Glass Mat Battery?
The newer type of sealed nonspillable maintenance free valve regulated battery uses "Absorbed Glass Mats", or AGM separators between the plates. This is a very fine fiber Boron-Silicate glass mat. These type of batteries have all the advantages of gelled, but can take much more abuse. These are also called "starved electrolyte.” Just like the Gel batteries, the AGM Battery will not leak acid if broken.
What are the advantages of the AGM battery?
The advantages of AGM batteries are no maintenance, sealed against fumes, hydrogen, leakage, or non-spilling even if they are broken, and can survive most freezes. AGM batteries are "recombinant" – which means the Oxygen and Hydrogen recombine inside the battery. These use gas phase transfer of oxygen to the negative plates to recombine them back into water while charging and prevent the loss of water through electrolysis. The recombining is typically 99+% efficient, so almost no water is lost. Charging voltages for most AGM batteries are the same as for a standard type battery so there is no need for special charging adjustments or problems with incompatible chargers or charge controls. Since the internal resistance is extremely low, there is almost no heating of the battery even under heavy charge and discharge currents. AGM batteries have a very low self-discharge rate (from 1% to 3% per month). So they can sit in storage for much longer periods without charging. The plates in AGM's are tightly packed and rigidly mounted, and will withstand shock and vibration better than any standard battery.
Side story: On the way to pick up the batteries, I won $100.00 on a Texas lotto scratch off. So, I really bought both batteries for the price of a regular Academy battery.
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