What i have figure out from iphones is the battery is not calibrated correctly.
What I do, and this gives me the "best battery" possible, is 1) the first day I have the phone dont let the battery die completely, use it till about 30% 2) charge the phone overnight 3) use the phone next day until battery is so low the phone no longer turns on What you will notice is that the battery will drop quickly at first then it will slow down (it will go from 90 to 80% in 1 hour but go from 10 to 5% in 3 hours). 4) charge fully again next day and use normally. That will tell you how good the usage is and if the battery size fits your needs
People post battery results with 20% remaining complaining that they only get 3 hours. Well its probably because your phones battery is not calibrated with the circuit that reads capacity. Discharging and recharging from 0% doesnt add battery capacity but it does make the percentage meter more accurate.