charge up vs step up

charge up

verb
  • To motivate, to instill someone with determination. 

  • To recharge, to give electrical power to something. 

  • To deliberately infect an individual with HIV as part of bug-chasing. 

step up

verb
  • To increase, augment, or advance, especially by one or more steps. 

  • To assume or take responsibility. 

How often have the words charge up and step up occurred in a corpus of books? (source: Google Ngram Viewer )