lime battery

we wanted to see how a battery worked we put a zinc nail and a piece of copper into a lime and connected it to a volt meter

1 lime =0.95 volts
2limes=1.96
3limes=2.9 volts

and the 3 limes lit up a led


questions does the size of the lime matter/?

what if I put more nails or copper on/yes

can I use different metals/no

later we used a banana wich was more effective by producing 1 volt