“Healing Is Voltage” is an insane treatise by quack doctor Jerry Tennant, who claims that cells operate within certain voltage ranges, and that we must measure the voltage of our organs, and apply external voltage to them to treat our diseases. Considering the book begins with a rambling 10+ page prologue complaining about Microsoft Word, the Oxford comma, Adobe, the separation of church and state, Wikipedia, boxing, the Constitution, and the Boy Scouts (hit the Look Inside link if you want to read it for yourself) you can safely assume it to be quackery.
Also, there’s the small detail that -20mV, which he claims to be “healthy”, is a lot lower than the electrochemical potential across the membrane of any functioning human cell. And cells have to maintain this gradient by using ATP to transfer cations (not electrons, as he claims.) But you probably don’t actually need an actual biochemical explanation of why alternative medicine is insane.