After accumulating several hundred recycled 18650 cells from laptop batteries, I need an affordable way to test each cell’s capacity for reuse. I would use decent cells to make power banks, small battery power generator, camping lights, and other projects. For projects require higher current output, like my DIY electric mountain board, I bought new 18650 cells capable of producing higher amperage. To test the recycled 18650 cells, I designed, and 3D printed housing units while using electronic modules purchased from eBay.
As I was looking for a way to make the contacts between the 18650 to the terminal of the wires, coincidentally my coworkers humorously gave me 100 pennies instead of a dollar refund. To their surprise, I was happy to accept it. Right away I knew that I could use these pennies to make the terminal connections.
The U.S. pennies made before 1982 are 95% copper, with a few exceptions. You can get a detailed list from this wiki article: (https://en.wikipedia.org/wiki/Penny_(United_States_coin). I found 20 pennies made before 1982 from my stack of 100 pennies. I’ll probably be using pennies made after 1982 when I make more of these chargers. Pennies made after 1982 are 97.5% zinc, and it is still conductive enough for this project.
The process is simple, charge each cell to 4.2 volts and draw a constant current until it is discharged at 3.2 volts to get its capacity. Each charger is an electronic circuit module used to charge a 18650 cell. It’s similar to the one inside those smaller portable batteries. I got 10 of these TP4506 lithium chargers for $5 from eBay.
And the capacity meter discharge ZB2L3 from eBay:
Here’s five 18650 cells being charged at 1A:
Here’s five 18650 cells being discharge at .5A: