With nothing else to do, I wanted to see if I could make a flashlight out of pennies. Since pennies after 1982 are mostly copper coated zinc they have the potential of making a battery.
The first step is to sand down one side of the penny. I placed them close together on a strip of gorilla tape wrapped sticky side up around a board then used an electric sander.
Once you have all your one sided pennies filed down. Cut out circles the same size as the pennies out of cardboard, paper. Cardboard last the longest because it takes longer to dry out. Make enough circles to go between however many pennies you sanded down. I am stacking about 10 pennies together, but you can experiment with more. Theoretically, the more pennies you use the higher the voltage.
The hard part is over, now it is time to assemble it.
Stack all the pennies facing the same way with your cardboard or fabric between them. Then place the leads of the LED on opposite sides of your battery and bind it all together. I used Gorilla tape here and electrical tape in the past.
Now that your flashlight is complete we need to get our acid. Here I am using lime juice from my fridge.
Dip your battery end in the lime juice so that the cardboard or cloth can soak up the acid. If your LED terminals are making a solid connection it should light up in a few seconds.
They rarely light up for me the first time I make them. I have to squeeze, bend, wiggle, and adjust the leads until it does.
They only lasted a few days because they dried out and had no conductivity. Perhaps if you could seal the battery part in a protective covering to keep it from evaporating it would last much longer.
I would solder or weld the leads to the end of the coins. Sometimes it is hard to get a solid connection and they will shut off intermittently, or only glow when you put pressure on the leads.
The last thing I can think I would do is to stack way more pennies together. I tried this once with 20 pennies but it did not work. Either the large amount of tape I had to use shorted it, or the wires I used to connect to the led leads didn't have enough conduction I suspect.