Lime Battery

We wanted to see how a battery worked. We put zinc nail and a piece of copper into a lime and connected to a volt meter.
1 Banana=1 volt
1 Lime=0.95 volts 
2 Limes=1.96 volts
3 Limes= 2.9 volts and it lit up a LED

So does it depend on the size of the lime?
What if I put more nails and copper in?
Can I use different metals? 
Can you put more wires in? Yes
https://www.youtube.com/watch?v=GhbuhT1GDpI

Electronics

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