I made a device to track battery discharge pattern, it works with Arduino and INA219 Sensor, as you can see in the schematic, the system is wired somehow with a common GND, when I put one battery in the device, it works as I expected with 3.9 Ohm resistor in the path, but when I add second and third batteries, the sensor output changes, it results in either decrease in voltage of the first battery or the current, therefore, calculated resistance changes and increase accordingly, can someone suggest what is wrong in here?


the schematic


Note: I guess the common ground in between batteries makes the first battery works as a new path for the second and third batteries, therefore, we see such thing, I thought maybe a diode between the battery and common GND may solve the issue, but it needs a heavy work to destroy everything I made, so I am not sure about it, am I correct?

device



output result

 

It may be you need to have just one GND point to ensure no current flows in any GND wires other than the battery under test.
Do not share wires between the 3 discharge paths, or their monitoring circuits.

 

Do not share wires between the 3 discharge paths, or their monitoring circuits.

can you please elaborate on your answer, because I think I didn't do such a thing

 

Something like this.
Same connections but each device has a unique current path so they do not interact.

 

Same connections but each device has a unique current path so they do not interact.

Hmmm,
So, basically, my guess about interacting batteries with each other is correct then!