That's pretty good voltage, volts happen almost without trying.
In the same way that they just happen, you can see them disappear too, it's strange.
Try 3 nails with a rubber band around them, wrapped in a paper towel.
Then wrap the copper wire around the paper towel.
You should get a bit more amps from that.
It's the amps that are harder to obtain.
That is surface area, distance between metals and solution dependent.
Solution, other than just water, will cause your metals to be used up faster though.
I cut the top off a fresh Aluminum Can, 12 oz., and tested it as is .. ZERO amps.
I burnt off the inside coating, do this outside. I'm sure the fumes are toxic.
It read 0.4+ mA, I'm using a lot
of copper wire.
Cut the bottom off the can and down the side making it a sheet.
Cleaned the burnt coating off.
That read 0.35 mA .. loss of surface area due to the bottom of can being missing
hurt the reading. I didn't get a reading before cleaning, only after, whoops.
Wrapped my copper wire in paper towel and the sheet around that.
That read 0.43 mA . The closer the two metals are together more the output.
The issue is evaporation of solution in long term use, in small compact cells. It goes really fast.
Ease of construction is a factor and connection of cells is a problem ..
It would be nice if connectors could be constructed. I've managed to create
negative connectors out of Aluminum Can, the Aluminum is the negative in these
cells. I need to figure out a way to do away with soldering wires to the positive side.