If you use copper coin every cell will produce .7 to .8 volt 2 – 4 ma.
for 5 volt we need at lest 8 cell
So if you want to charge you mobile phone at 500 mp
you need 500*8 = 4000 coin.
I don’t have this much coin but if you make this much cell definitely it gonna charge you phone.
See video… https://www.youtube.com/watch?v=b3aSwT-p__A