Adding Multiple I2C lines to Arduino Board

I am currently working on a project that will require me to measure the voltages of 48 batteries, convert the analog data to digital, and then transmit that data through an Arduino to a computer. I have found an ADC (ADS1115) that will allow me to take differential inputs, so reading 2 batteries at a time (I will need to do differential inputs because the batteries will have floating voltages). The problem I am going to run into is that I can not figure out a way to add more than 4 ADC’s to the Arduino board through I2C connections. Is there a way to increase the number of I2C connections or is there other compatible ADC’s that offer more inputs? 

Did you look at this, this or this ?