It's not uncommon for 4 cell batteries to run a lower voltage than 3-cell batteries, and this model shows support for both.  As long as you're buying an OEM battery, it will work fine. [URL]  
I have a latitude 7390 2-in-1 that has a 45Whr battery model 71TG4. I know that this laptop also support 60Whr battery model K5XWW. However, I am unsure if I can upgrade from a pre-fitted 45Whr to 60Whr because the 42Whr battery has 11.4V output and 60Whr battery has 7.6V output.  Please advice. As i will really like to upgrade to longer lasting battery.[IMAGE]45Whr batt[IMAGE]60Whr batt
Latitude 7390 2-in1 Battery from 71TG4 to K5XWW