Regarding using AGM batteries in a closed area. If you do not have some kind of forced or a natural convection form of ventilation, 24/7 it is not really considered vented for the small area you are using. Should that ventilation stop, all bets would be off, and muffin fans are not 100% dependable. I would not be willing to risk even a SLIGHT chance for the possibility of an explosion. Do they have a hydrogen gas monitor/alarm that could be mounted in the battery compartment?
Here is a response I received from USBATTERY MFR, Eng Dept:
AGM wording on our website reads as follows:
Hydrogen gas emission is less than 4%, allowing U.S. Battery’s AGM products to be used in aircraft applications and in areas with enclosed spaces (but not in sealed or gas-tight containers).
AGM batteries can vent hydrogen and oxygen under certain conditions and should not be sealed into a gas tight container. A spark inside the container could result in an explosion.
Hydrogen is a very light and mobile gas and will dissipate rapidly as long as the container is vented.
U.S. Battery Mfg. Co., Inc.
1895 Tobacco Road
Augusta, GA 30906
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