Connecting Multiple Voltage Sensors (Dumb Dad Needs Help with Daughters Science Project)

I have decent understanding of using Arduino boards and sensors using one analog input. But, I have researched for hours and am kind of lost on connecting multiple voltage sensors. Here's the project and why we need this.

My daughter wants to measure how long a single AA battery lasts to determine which brand is most cost efficient. She is in 4th grade, and this has been done before using visual observations, but she wants it to be more precise. We could put my GoPro on and try to record the entire run time, but I feel that just isn't the cool way to do this. So, I said lets use Arduino! I was thinking we could measure six battery and load setups using an 0v-25v sensor connected to the six analog ports on the Uno. I know I can only read one sensor at a time, but this really isn't an issue because we are trying to narrow the visual observation down to seconds.

Each sensor reading is basically its own experiment, so I thought the connections would be something like: connect positive battery terminal to ground of 0v-25v sensor, connect Vcc of sensor to fans positive terminal, then connect the fan negative to battery negative. With this setup I am hoping that once the fan turns off, the sensor will read a negligible value indicating that the fan stopped working. If that works, then my next concern is properly connecting the 6 sensors to the UNO. I believe each sensor needs to be grounded to the Uno board so the APC can read the results and I am concerned that this will be a problem amongst others that I am probably not skilled enough to think of.

So that's basically where I am at in trying to plan this out. Any help, ideas, or thoughts are greatly appreciated!

So each AA cell is powering a small fan?

I would connect all the cell negative sides together and to the negative sides of the fans and to Ardiuno ground. Then the positive side of each cell goes to an Arduino analog input pin (A0-A5) and to the positive side of one fan. The Arduino can then time how long until each input crosses some thresholds, like 1.4V, 1.3V...

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Yes, its a dollar store handheld fan. If I am reading your suggestion correctly, I wouldn't even need the 0v-25v sensors and just use the Arduino's built in voltage sensor. Is that correct?

Correct. I don't even know what a "0V-25V sensor" would be. For a 1.5V (nominal) AA cell the analog inputs of an Arduino UNO, Nano, or Mega would be sufficient.

If you have a LOT of cells to tet, the Mega might be a good choice because it has 16 analog inputs and a 2.2V internal voltage reference you can use to get better resolution.

Thank you for the advice. I will try get this setup working tonight.

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