A while ago I wrote a simple Python script to do this testing with an airplane/drone flight controller (they have voltage and current sensors onboard) and a constant load. Here are some of the curves I did of my batteries:
What‘s the easiest and hopefully cheapest way to get a setup where I can do theses tests myself?
Is there a charger / discharger with a USB interface that will let me access this data?
Hm the cheapest cheapest way is to discharge the battery to 3V and then charge it up again with a charger that tells you how much energy went into it. I'm afraid I don't know of an off the shelf way to get the curve, though... The way I did it isn't too hard, but it isn't the easiest either.
I think I‘ll try adding Bluetooth to my old Imax B6 charger to get that data.
Looks like Atorch DL24 battery tester can be used for that at a cost of around $22 or so. And the Tuya BW150 also has WiFi in and acts as a HID device for a couple bucks more.
https://notes.stavros.io/maker-things/battery-discharge-curv...
And here's the script itself:
https://gitlab.com/stavros/assault-and-battery/
As you can see, it's very easy to tell a new, genuine battery from an old or fake one.