Typically that means the posts are leaking vapors through the post seals. The cause of the seal breaking is over torquing the the nut and not holding the post while tightening. The vents on the caps are made not to vent towards the posts . You don't need to make the nuts super tight. They only need to be snug. You hold them to counter torque.
Remove the connector and run a thin layer of RTV around the base, sealing the case to the post. Put some vasoline on the inside of the post and reinstall. You want to get the posts done before the RTV cures. Smear some vasoling on the post connectors when done.
People argue with this until they have seen it done. I been doing this for a week and a half. LOL
There is one issue to consider when using silicone - it is very hard to remove if required in the future. Vaseline works. Marine battery terminal spray, also.