Shinny copper pennies
Wires with alligator clips on each end (2+ per battery)
and cut it in half. This will make 2 batteries. Potatoes are juicy, which is part of the reason they can be made into batteries.
Take a knife and put a slit in the potato and slip the penny into the slit. Push as much of the penny into the slit as possible, you want just a little bit sticking out of the potato. Push the nail most of the way into the potato,(at this point I cut the nails in half, so that they weren't so tall). Do not let the electrodes touch, keeping them about 1 inch apart.
Turn on the Multimeter and put it at the lowest voltage reading. Make sure the red probe is in the + slot and the black probe is in the – slot.
Use the red line to touch the penny in the potato and the black line to touch the nail. You can read how much voltage you have available in this potato battery. It reads .85 volts, not bad but not enough to do anything fun.