Ayla, You should be able to use the ADS1115 to measure a lithium ion battery voltage. For this application you should also be able to power the ADS1115 from this battery. However, an error of ±100mV seems very large. If you are using the ±4.096V scale, the offset might be a few LSB, and the max gain error would be about 0.25%. This is from adding the max gain error of 0.15% at ±2.048V range and then adding the 0.1% gain match specification. With this measurement, I might expect a max error of about 10mV out of a 4V measurement. Note that even with the differential measurement and getting 15bit resolution for positive measurements, you should be able to get good results. I don't think that a differential or single-ended measurement (as set by the configuration register) would make much difference. For your setup, how do you have this ADC configured? Can you share a schematic? What multimeter are you using for corroborating your results? Because I think this measurement should be much more accurate, I'd like to try to debug this circuit and measurement. Joseph Wu
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