hksmonaro:
. . .
So from a potential highest possible voltage I should be within boundries if I was feeding the ADS1115 with 3.3v or 5v?. . .
That is true, providing of course that the ground remains intact.
You can, incidentally, get purpose made battery management chips:
Maximizing Cell Monitoring Accuracy and Data Integrity in Energy Storage Battery Management Systems | Analog Devices (figure 4 appears to be what you are trying to achieve but I can't say how suitable it is)
The chip is https://www.mouser.ch/datasheet/2/609/680412fc-1271800.pdf (~$20 )
By the way, I love the smoke detector in your picture. Hasn't the Boeing Dreamliner got a similar battery installation?