I started out , when at work they had pile of battery packs for laptop computers , that no longer worked. Well I know that most (not all ) Battery packs for Laptops are made up of a bunch of 18650 Li-Ion Battery Cells , and it is usually only one or 2 cells that go bad in a Pack making the entire battery pack no good. So I grabbed a Bunch of them and took them apart. My use was going to be to use them to power some Bicycle lights. Figured I would charge them up and shouldn't be too hard to find the bad cells using an Volt/Amp Meter , this Worked but not well by any means ,I soon discovered that a lot of the cells would take a charge , but not much of a charge , found this out the hard way with bike lights that went dark too fast.
So I came up with this Idea of using a Computer , with an analog input, and would read the out put of the battery across a load over time to determine how much energy the battery cell could store. My first attempt was using an old PC with a Metrabyte DAS-8 A/D board . It was basic , I would manually connect the load start teh data collection, stop it after time , and then using excel determine the amount of energy in the Cell. But I wanted to do this more automatically . I was using an Ardunio for another project ( which will soon have an instructable for it ) and realized it had all that I needed to do this . so I made the switch and it was a lot easier to wire up , program and took up a lot less space.
Step 1: Charging The Batteries
Charging LI-Ion Batteries
WARNING WARNING WARNING
when charging LI-ION batties Be careful! they can be unstable and catch fire. I have never personally had this happen , but I don't care i always take the precautions, better safe then sorry. there are plenty of horror stories out there.
1) Never Charge unatteneded!
2) Charge out doors or some place some place pretty much fire proff ( I charge mine on the Bricks of my fire place or top of Steel sheet )
3) AVOID drivect shorts
4) do not use a Physically Damaged Cell.
5) Dispose of Properly ( I take my To Home depot and deposit in there battery recycling bins )
Most of the time I use this simple charger from Deal Extreame ( http://dx.com/digital-li-ion-18650-battery-charger-6105) I also will use a larger RC Smart charger for doing multi cell packs , but that is a little beyond what this Instrucable is for.