I found out my problem I believe and it still amazes me. I had a Honda trunk liner (vinyl or plastic or? .... some synthetic black stuff) It's basically to protect the trunk ... kind of like floor mats. Anyway I removed it and in a weeks time the smell was gone. The liner is in the garage now and it still smells like a leaking battery. I think in the heat of the trunk and the three plus years it's been in there it finally decomposed to a certain point and began out-gassing. The car doesn't smell at all now but the garage does. I think my battery is fine.

 

Well its good you got it. Thanks for sharing! Hal

 

Good to hear you figured it out!

(And sorry for the paranoia)