I have still not read a book about The Battle that is as good as "Duel Of Eagles" by Peter Townsend.
This book is by a man who is not only a terrific writer, he was an ace during The Battle. He knows of what he writes!
He doesn't simply tell you about the Summer of 1940. He goes back to 1918 and covers how the RAF and Luftwaffe were formed, and how they came to meet over the skies of England. If you only read one, I really this this should be it.
"From our orbital vantage point, we observe an earth without borders, full of peace, beauty and magnificence, and we pray that humanity as a whole can imagine a borderless world as we see it, and strive to live as one in peace."
Astronaut William C. McCool RIP, January 29, 2003 - Space Shuttle Columbia