Measure LiPo Battery Cells with Voltage Divider?
You will need to connect the "bottom" of your voltage divider to ground, but do not make any additional connections between ground and your batteries.

So, you will need to use four voltage dividers. The first will measure the voltage from cell 1, the second will measure the total voltage of cell 1 + cell 2, and so on.

In your software, measure the voltage for cell 1. You will need to convert the ADC reading to the actual corresponding voltage. Now measure the voltage for cell 1 + cell 2. Convert the ADC reading to actual volts and subtract the previously calculated voltage for cell 1 alone. Now you have the voltage for cell 2. Repeat for all four dividers.