Another Heaviside biography in addition to the one cited in the
article is "Oliver Heaviside: The Life, Work, and Times of an
Electrical Genius of the Victorian Age" by Paul J. Nahin. It's
profusely illustrated and doesn't omit the math.
"The best result of mathematics is to be able to do without it", he said, which seems strange but makes sense coming from the man who came up with functional operators.
I knew this quotation in my undergrad school days; just now checked the net and there is a source: https://hsm.stackexchange.com/questions/7332/a-peculiar-quot...
See also The Science of Radio And the Mathematical Radio (Similar content but one more focussed at elec eng people and one more at math(s) people)