I've been doing a little research on the earth batteries of the 1800's. Very interesting. I managed to light a single LED light with a series of 8 cells consisting of sand, plastic cups, a graphite rod, and some alloy metal (I'm not sure of the exact composition). I set it up similar to an old wet cell; graphite to the alloy metal immersed in the sand which was in a plastic cup, making a total of 8 cells. The total reading on my multimeter was areound 6-8 volts, it didn't exactly remain constant. The LED did not shine brightly either, nonetheless light was still being emitted. When I tested the voltage entereing the LED though it was only around 3-4 volts. The current was extremely low, only around .1 mA. I can't really see any practical use for something like this, but I still find it fascinating that it actually works.