I needed:

I took two glasses., a copper wire, a piece of aluminium foil and metal wire and three cables. A quarter glass of boiling water and ¼ glass of  common salt. 

What I did:

I  twisted a piece copper wire, I folded the foil in a shape of a square. I joined one cable to a piece of  aluminum foil, and the second one to a spiral of copper wire, and then I connected them to the metal wire. 

I reinforced the connections with a strong tape. Then, I repeated the whole procedure once more. Finally, I connected those two parts with the aid of the cable and metal wire, and I placed them in two separate glasses. 

I made a solution of boiling water and salt. I poured the solution into two glasses. I connected the ends of the cables to my mobile phone. The current was generated and in this way I charged my mobile.