I read a book years ago in Junior High. I am wracking my brain trying to remember more details. It was possibly a young adult novel, since I read it in middle school or early high school in the late 70's or early 80's.
It was set in the future, but in a pseudo-medieval setting - something had happened and there was no electricity. I think also no records about history from before the event.
There was however a secret society that knew about electricity, science and history. Christianity was another one of the things that was known only to the secret group.
There was a death caused by electricity in a bath tub. It may have been accidental, or it could've been a murder. I'm not sure, but the electric item might have been a radio.
Sorry the details are so fuzzy, but it's been 30 years or so since I read it.
It isn't The Long Tomorrow, (I read it since someone suggested it), and A Canticle For Leibowitz sounds more complicated than what I remember and what I would imagine I'd have chosen to read back then.