While our users may be able to help you out here, we hope that you also will take the time to check out our six-part series, "Finding and Understanding Sources", which should hopefully prove to be helpful for you as you continue in your research.

Although I likely can't help much with the actual books, is there any more specific detail that you're most interested in? As in, are you looking at the immediate reasons why it was dismantled, or more long term 'decline' of the HRE? I'm sure there'd be very different recommendations based on which one you're trying to find more about.

There is a new book that came out, "The Holy Roman Empire: A Thousand years of Europes History" by Peter H. Wilson, and I pre-ordered it. It covers the entire HRE period from start to finish and it really is stunning. I'm half-way through, and the book does a good job not only in explaining the sheer complexity of the Empire but the political, religious and social issues it faced.

I was also unable to find any overview level books in Portugese. :/ But I did find this: An academic forum for HRE researchers. It has many resources gathered together, which should help in your research.