Here's my setup:

* Raspberry Pi 3A+
* [52Pi EP-0118 Raspberry Pi UPS](https://wiki.52pi.com/index.php/UPS_(With_RTC_%26_Coulometer)_For_Raspberry_Pi_SKU:_EP-0118)
* [ADS1115 ADC](https://rads.stackoverflow.com/amzn/click/com/B07KW2QZS2)

I'm trying to measure 18650 battery voltage of the UPS. UPS in question does provide voltage reading, but on the output of the regulator. Strange choice, given that the whole point of the regulator is to output stable 5V. Anyways, since RPi does not have an ADC, I thought I would hook one up to it. My wiring is:

* ADC V - 5V Rpi
* ADC G - Rpi G
* ADC SCL - Rpi GPIO 3
* ADC SDA - Rpi GPIO 2
* ADC ADDR - Rpi GND (not sure if this is strictly needed)
* ADC A0 - Battery + terminal

Without hooking up A0 to the battery terminal, UPS and Raspberry Pi turns on just fine. As soon as I hook up A0 to Battery+ two things happen:

* RPi Power LED turns on along with UPS RPi Power LED
* UPS refuses to turn on, acting like there's a short in the system

I must admit I'm pretty new to using ADCs. I was under the impression that the wiring here makes sense - ADC, RPi and UPS all share common ground, and hooking up Batt+ to A0 would allow it to measure potential. Apologies in advance if I'm doing something obviously stupid here. Any advice is appreciated.