Originally Posted by killarney_sailor
Because of the configuration of our batteries, we need to use sealed batteries. I have always thought that AGMs were superior to gels. Is this true?
No not really...
GEL batteries are the kings of cycling and they can be some of the longest lasting deep cycle batteries made, in typical marine format. It is not just me who understands this Sandia National Labs has shown this true in government funded independent studies.
GEL's do however require a lower absorption charging voltage, 14.1V, and a higher than normal float voltage of 13.8V. All charging with GEL batteries should be temp compensated. This is not something the typical boater can do easily without system upgrades.
If you do these things GEL's will last a long time. Deka/East Penn rates their GEL batteries at 1000 cycles and their AGM's (depending upon your inside source) at just 300-350 cycles. This is using the same test criteria for both batteries done by the same manufacturer. For Deka GEL batteries this means up to 3.3 times the lab rated cycle life over their own AGM.... If your batteries could last 3.3X longer......
The reason GEL's went out of fashion, so to speak, is that Deka and others tried to tell folks they could be charged at regular flooded lead acid voltages. This quickly destroyed them and gave GEL a very undeserved bad rap. Deka then recanted and for 20+ years said 14.1V and 13.8V and this works beautifully and we have lots of GEL banks lasting well in excess of 10+ years. I have one bank in its 15 year and three or four beyond 10... I have no AGM banks beyond year 7-8 at this point in time and that is not because the owners have not tried.
Now that their market share on GEL has plummeted, and been eaten by AGM, which is giving them another bad rap on longevity, they have once again begun telling people it is okay to charge GEL at higher voltages.. "Stupid is as stupid does."....
My buddy Bruce sailed around the world TWICE on the same set of GEL batteries. I don't know of any other double circumnavigation with any other battery type out there. Perhaps there are, but that feat is damn impressive especially considering the abuse he put them through.
AGM batteries certainly have benefits, such as high charge acceptance, but long cycle life, beyond a typical deep cycle flooded battery, is not necessarily one of them. Premium AGM's can have decent cycle life but it requires dedicated patience & a good system to get there.
All sealed valve regulated lead acid (VRLA) batteries require a proper system approach to use and charging..