As of many hackerspaces we rescue 18650 cells from old laptop batteries and other sources
We do have a charger but no good way of testing the capacity of each cell before it goes into the parts pile
Making a capacity tester would solve this. One could buy a chinese unit from fleabay but where is the fun in that? :)
partlist:
- Arduino pro mini - Display - Button - TP4056 module - 18650 battery holder - 5v relay - DC current load \ - Logic level N chan mosfet - lm385 opamp - 50k 10 turn pot - 1 Ohm 5 Watt resistorrrr