Sunday, Mar 05, 2017 at 13:26
The modern sealed maintenance free rugged construction battery .... it may have "marine", " earthmoving" or "4wd" printed on it pretty much has the following.
Heavier and or more plates with wrapped or packed with glass mat, to dampen the plates from vibration and to stop the electrolite slopping around and getting agitated and to retain the electrolite with the plates in other than flat and level situations. ......... not unlike an AGM battery.
Calcium, possibly antimoniy and other possibly propriatary metals have been added to the plates to reduce gassing, increase life and improve performance in general ...... not unlike AGM
Changes in electolite chemisty to compliment the changes in the plates, to reduce gassing, promote recombination, surpress sulphation, increase life and improve performance in general .... not unlike AGM.
What sealed maintenence free rugged construction batteries don't have is all the free electrolite tipped out ( which is what an AGM battery is) ..... because there remains an ample surplus of electrolite in the battery it will withstand heat and certain types of abuse better than most AGM.
Pretty much all the technologies that allow AGM to exist are employed in all sealed batteries to a greater or lesser degree.
In my opinion AGM is heavily oversold and in many situations of no benefit and of no advantage in most situations.
One thing AGM does have, is the ability to travel in and be stored with general freight ...... so there are a lot of companies that can and will sell you nothing else, because they do not have the facilities to store or transport wet cell batteries.
AND because AGM sells for twice, of an equavalent wet cell ...... good salesmen can make at least twice as much selling you AGM.
Then there is this "Deep Cycle" thing ..... many people have the eroronious idea that deep cycle will withstand being heavily discharged better ....... this is not the truth ...... deep cycle is designed to withstand being at lower states of charge for longer and to deliver low discharge currents over a long term more efficiently.
Hammer a deep cycle day after day, it will die just as quickly as a similar normal battery.
Most RV uses, the battery use is short term cyclic discharge ...... being hit fairly hard over a day or a few days and then hammered up to charge as fast as possibly ....... this is half way between a deep cycle application and a starting application ........ this is exactly what marine batteries are expected to deliver .....
The actual situations where AGM is actually required or of any real benifit would be very few indeed.
cheers
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