Join Date: Apr 2006
Location: Spokane, WA
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AGM batteries are known in the industry as VRLA (valve regulated lead acid). These batteries have a stringent charge requirement to prevent a condition known as thermal runaway at high temperatures and maintain full charge at low temperatures. Without the proper charger these batteries have been known to explode at high temperatures (such as a boat in the sun w/o ventilation). Admittedly, these explosions have happened as far as I know only in industrial settings. I have never heard of one happening on a boat, but there is always a first time. I have yet to see a marine charger with temperature compensation (lowering the float or charging voltage at high temperature and raising it at low temperature). They may be out there, if so, those of you who have sealed batteries should invest in one.
As an electrical engineer who has specialized in DC power, i.e. battery charging, I have flooded (or wet) cells on my boat. They can take much more abuse; can tolerate a deeper discharge, more discharge cycles, higher & lower temperatures then sealed batteries. Wet cells vent the hydrogen that sealed batteries store, under pressure, within the cells. That does not mean that sealed batteries don’t vent, that’s what the valve is for, to vent pressure, i.e. hydrogen that builds up during use/abuse. A good wet cell should outlast a AGM cell considerably. Just make sure the water in the cells is always topped off.
Always vent the battery compartment, weather you are using wet or VRLA batteries, to the outside to prevent hydrogen gas build-up. Hydrogen is very volatile (explosive) but fortunately is lighter then air.