So, here is a simple way to make a low powered battery for under a dollar.
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Step 1: Getting the Stuff Ready
5 american* pennies w/ dates between 1945ish - 1980. I'm not sure if "wheat pennies" work.
A cup of vinegar - Salt water works too, just not nearly as well.
* - According to one user, it can be made with the European 10¢ coin.
Step 2: Prep
Start by cutting the cardboard into 5 circles smaller than a penny, but not too small
Then, put the circles in the cup of vinegar
Cut the tin foil into circles of the same size
Step 3: Assembly
Put one tin foil circle down, then one cardboard circle. Next, put a penny on top of them.
Repeat this step until you have a pile of them. The cardboard cannot touch! Keep everything uniform. once done, put a lead of an led on one end, and the other on the other end. If it doesn't turn on, switch which end the leads go on. If you still don't see any light, make sure that no cardboard is sticking out/touching.
Step 4: Done!
Congratz! If you made this, please click made this at the top of the page, and post a picture of it!
Step 5: Troubleshooting
If a piece of cardboard touches another piece of cardboard, it won't work.
If it stops working:
Re-soak it in vinegar for 1-2 minutes. Don't worry, if the LED is already on, it won't make it break
Let it drip after being re-soaked. It may take up to 30 seconds of dripping to get all the water off. Excess water shorts it in a non-dangerous way.
Re-adjust the way the LED sits on it, it can be finicky.
Also, some people say this has stayed on for 16 days for them. I got it to stay on for 10-12 hours. Thestalkinghead claims to have gotten it to go for 43 hours(Almost 2 days!). Post in the comments how long it runs for you(time between soaking it and the led not being on).