Fairly new to this but why is it when I hook up my 2S lipos to my cell checker they both read 4.15v with a total of 8.3v? Where does the 7.4v come from?

7.4V is the nominal voltage. A full charged lipo is 4.2V/cell, or 8.4V for a 2S.

Typical for a battery, the full charged voltage is higher than the nominal voltage rating. Nominal is more of an average voltage under load (while being used).

You're good.

Makes since. Thanks