[Monkey Wrench]

ive seen lots of cars with rusty battery boxes, although batteries are generally sealed somehow acid gets out.

i just soak a cloth in baking soda and water let it dry, and place it under my battery that way any acid gets neutralized immediately.

ive never had the issue of the pad becoming water soaked and retaining water.

in a former life I had to maintain electric forklifts , they have huge lead acid batteries that can be swapped out. part of regular maintenance was to give the outside case a wash with a paintbrush and baking soda and water. also wed check the specific gravity and add distilled water when needed..
that way you aren't wrecking your clothes or walking away wondering why your arm is burning , or replacing your pants due to holes.. most of us here have probably wrecked some clothes that way at some point.

also I lake to keep a box onhand. its cheap and can neutralize an accidental spill.
gel cells or similar that aren't vented and are well sealed may not need the pad I guess.. If I spilled acid I'd run for the box..

I think most lead acid batteries, although they may not have easily removable caps like older ones, still need some sort of vent, so they can't explode by pressure building inside when charging or by expansion and contraction with temperature changes.. and things like that. the acid may leave slowly that way.. maybe just by air within moving to outside the case. I guess some have a vent for that.

Do what YOU prefer of course, but thats my way .. I don't need any special pad, just a face cloth will do.

if you think the battery compartment gets wet because its near the vent cowling etc, maybe that is a different concern.. my suggestion was not to add a wet pad, let it dry out first. I've been keeping my 944 in a tent so its not wet and that was not a concern but I do think I remember it had a drain hole around the compartment somewhere.. maybe its susceptible.. my compartment looked decent , not rusty when I got mine and it sat outside a lot before then so it didn't look like a wet area to me. Here
In vancouver there is no shortage of rain lol..