Why can lemons power a mini watch (What we need to know)

1. What is the job of the acid in this case?

2. Can other fruits do so as well?

3. Does the metals that is inserted into the lemon matters?

4. What is the scientific explanation of acid?

5. How long can the lemon-powered mini watch last?

6. What type of acid do lemons have?

7. What are the benefits of powering a mini watch with a lemon instead of using a battery?

8. What is the whole scientific process behind this?