Nexus battery life comparison

The bigger the battery will/should last longer depending on the device:
Example: 3220 mah will last longer through out the day,Than a 2300 mah battery.

 

Battery capacity is measured in milli-amp hours (mah)
By definition, bigger battery capacity (in milli-amp hours) will certainly last longer than smaller battery, all other things being equal.
One tricky part is all other things are not always equal. Sometimes the bigger battery goes with phone features that tend to use more power (like bigger screen).

 

Different phones drain power at a different rate. In general, larger screens drain power faster than smaller screens.

There are also differences in screen technology. LCD screens use a back light and drains constant power no matter what is displayed. AMOLED screens have individual pixels that only light up when displaying something non-black. An AMOLED screen displaying a white screen will drain more power than displaying a black screen. Your colour scheme can take advantage of AMOLED screens by having a dark theme to save power.