In the story "Captain Marvel Battles the Red Lightning Blitz" we find Cap has flown to investigate a strange phenomenon happening in the midst of the Korean war. During his investigation, Cap is zapped by lightning from a lightning gun created by the villain the Red Crusher! What happens?!? Nothing! The lightning doesn't transform Captain Marvel back into Billy Batson!
I must note that I have seen two examples from golden-age Captain Marvel comics where Cap was transformed back to Billy by the electricity of a giant electric eel. There's also an example of Billy being transformed into Captain Marvel from a regular bolt of lightning. I have only seen screenshots of these so I don't know the entire story or context. (I'm trying to find what comic they came from so I can read the full story.) Additionally, in the 1970's Shazam! comics, there are two incidents where Billy and Cap both transformed after being struck by a form of magical lightning(Shazam! #15 and #31). Therefore, based on the burden of evidence, I have to conclude that the electric eel and regular lightning incident are errors or gaps in Cap's continuity. Who knows, maybe Zeus saw Billy was about to be struck by regular lightning and threw a magic lightning bolt at him to save him!!
Throughout Cap's comics, there are many times where it clearly states that it is the magic lightning that transforms Billy into Captain Marvel and back again. And, based on Captain Marvel Adventures #125 and #142, I can safely say that the only type of lightning that has any impact on Captain Marvel is the magic lightning thrown by Zeus!
*Based on Mike's Amazing World, this comic published on January 2, 1953.