Diagnostics test clearly wrong.

I have been to the iStore twice now with my iPhone 6 that i bought from the same store in October last year. This should mean that it is still under warranty. <br> My problem is that the battery has clearly been damaged in some way.<br> It went from being able to last atleast a day and a half to not lasting more then 2 hours on a full charge.<br> This is not my first iphone so i know how to properly charge it, and i even have an app to make sure i keep a good schedule. My iPhone 4 that is over 3 years old still keeps a charge with no problems.<br> <br> When i got to the store they connected my phone to wifi and started a diagnostic that said my battery was in good condition. This was the end of it, i was also told to make sure updates are off and the various other tips and tricks to save battery power which i have done because ive looked for the problem on the web.<br> <br> Clearly the battery is not in good condition and this is a major problem. The Guy that helped me was cool though, so with him i dont have an issue. <br> <br> I need something done about my battery, due to the nature of my work i cant be without my phone which keeps on dying on me.