Originally Posted by markdoane
As long as you keep the two holes in the door open it would be OK. You need one vent high and one vent low.
Actually, one hole high in the door is all you need, and one hole in the floor
that serves as both an inlet for air and an outlet for water. And elevate the battery slightly (about the height of a Lego block) so that water isn't trapped by the battery.
Also, shape the vent hole so that water is deflected away from the hole instead of dripping in. Easily accomplished by inserting a wooden dowel into the vent hole that is about the same diameter as the vent hole, then pressing down gently. This will slightly bend the top edge of the vent hole outwards, and the bottom edge of the vent hole inwards. This will help prevent water dripping down the door from getting in, though it won't provide perfect protection against wind-blown rain.
By the way, even battery boxes for AGM batteries are required to be vented. AGMs don't spill, but they can
outgas. They don't outgas as much as a wet-cell, but they do outgas. Which is why you can use an AGM in any position except upside down (if upside down, lighter-than-air hydrogen gas can't escape).