I would recommend against mentioning unrelated volunteer work in one's statement of purpose---after all, you have said that it is unrelated to the career that you are intending to pursue. If it were directly linked, then of course it would be useful to mention it.
Likewise, there is no space for this type of work in any of the main sections of an academic CV: this isn't like applying to college, where you are encouraged to list a bunch of extracurricular activities to show your breadth and interesting personality. Graduate admissions is instead more typically about showing that you have the mix of skills, drive, and focus necessary to succeed in you intended program.
It is often the case, however, that people will have some sort of "other significant experiences" section at the very end of their CV in which they put miscellaneous things that they think are important. If you feel that your volunteer work is an important ingredient in understanding you as a potential professional, then this is the appropriate place to include a brief note. It may help you if it catches the eye of somebody who finds it significant, and it is unlikely to hurt you.