I'm preparing the automated tests for creating the characteristic curves for tomorrow. I thought I had a proper 0.1 ohm shunt, but all I can find is an old wirewound cement resistor. It says "R15 10%", so 0.15 ohm. I'll use this for the 100 mA to 1 A tests.
For measuring the exact resistance, I used my SPD3303D power supply in constant current mode with 1 A limit and a BM257s to verify the current. Turns out the Siglent thing is pretty accurate, as you can see in the image below (too bad it doesn't have sense terminals for the voltage). Then I measured the voltage drop with my benchtop multimeter. Depending on where I measure it, it changes from 154.50 to 154.80 mV. Might need to solder some thicker silver wires to avoid this voltage drop, but I don't care about errors less than 1%, high precision measurements is a science of its own, will leave this to the experts.
Even after some time the resistor gets barely warm. Now the voltage drop is at 154.24 mV and doesn't change. So I can assume a resistance of 154.24 milliohm, which I will use as a calibration value when measuring the current with the initial setup I posted. Is this ok?
Next I'll replace the 8x1 mux with a 4x2 mux, to switch both multimeter inputs as close as possible to the shunt and the uCurrent and do some tests with a voltage regulator module I have here, which has a efficiency graph in the datasheet, and my graph should then look the same. Then I can just connect the Batteroo instead of my test module, run the script again, and we'll have a curve in no time