[Elecraft] how to seal holes in a car battery useable for /p operation?

[Stuart Rohre]

Tom and the group, Actually the original RTV (Room Temperature Vulcanizing)
Rubber sealant by Dow Chemical, Dow 732, did outgas acetic acid during cure.
You have to look for later formulations that emit an alcohol during cure in
place of the acetic acid.  Some RTV then emits acid, and some does not, the
label will tell for sure, read the fine print.

The acid is only a problem if the area where the sealant is used is not in
open air where the acid fumes can dilute and dissipate.  I have no idea how
they woud be in the presence of the sulfuric acid fumes of the battery.
There are also some rubber sealants, and you might even back up the place
RTV is used with a rubber bicycle patch or similar, to keep the battery acid
from contact directly with the curing RTV.  The air around the top of a
battery can have a high acid concentration as vapor.
73,
Stuart K5KVH