Simple battery tester


I am trying to make a simple battery tester by measuring the voltage supplied from four AA NIMH rechargeable batteries connected in series.

The circuit I have devised uses a voltage divider made up of two 10k resistors connected between the leads of the battery pack, I then measure the voltage between the resistors and simply calculate what the voltage supplied to the circuit is.

What I am wondering about is whether this circuit is correct or not. I am not sure if i am supposed to connect the negative lead of the battery to the ground of the arduino or not. As of now it is not connected, but the battery is in a closed circuit. Instead I connected a 10k pull-down resistor between the negative lead and the ground of the arduino.

My values correspond to the values I get when I measure directly with a multimeter so I’m confident that the setup gives proper readings, however is it a good setup? Or should I maybe connect the negative lead to ground?

The arduino is powered by usb.

however is it a good setup?

Most battery testers put some load on the batteries then measure the voltage. If you just measure the battery voltage you may be just measuring a surface charge.

Hi, you do not need the resistor from the battery neg to arduino gnd, just connect the two together and then you will have a proper 2 resistor potential divider.
The gnd ref of the arduino needs to be at gnd of the voltage source it is measuring.
Your two 10K are producing a divide by 2.
The extra 10k you have, has very little if any current flowing through it, so its volt drop is about 0V.
But for accuracy and consistency you don't need it.

Tom...... :slight_smile:

Remove the resistor to ground, then tie gnd from your batteries to gnd of arduino.

I think an arduino to measure battery voltage is like using a sledge hammer to crack a nut open with...

A 30cent comparitor for example will do the same job.... so hopefully you're doing more than measuring voltage :slight_smile:

Thanks for your answers, I will tie the negative lead to arduino ground.

And yes cjdelphi, it is being used for more :smiley: