When you aren't testing the battery life on your phone, do you tend to top it off whenever possible?
I find that I during the working day, I am either at my desk or in my car...in both situations I can keep it plugged in... I am not sure what that does to the battery life... Charging in this manner keeps the battery level between 95% and 100% back and forth all day... Weekends (and unusual business days) are different...
Today, I am testing my battery life, so even in the car with Waze and Google Play Music streaming to work, I kept it off the cord... But that's very unusual...I would never do that in normal practice...