Herold Weiss writes:
"Since the discourse that follows [John 5:18] denies the 'Jewish' understanding of the equality of the Father and the Son, is the 'Jewish' charge that Jesus had broken the sabbath to be taken seriously? I suggest that in John's view the 'Jews' are wrong both in their understanding of the equality of the Father and the Son and of Jesus as a sabbath breaker."
See "The Sabbath in the Fourth Gospel," Journal of Biblical Literature, Vol. 110, No. 2. (Summer, 1991): 311-321.