Hi, I have an iPhone 6 since launch day. Super happy with it and I hope to keep it for at least one more year, unless I broke it. However I'm quite disappointed with my battery. Over the last couple of weeks I have noticed I need to charge it more often. Before a charge could easily go for 2 days now I end my day with 20% to 30%. I get it, it is normal that the battery loose capacity over time and it is not a huge deal, still holds the complete day. Is there something I could do such a calibration ? If not how much does Apple charge in the US to change the battery ? And which battery case I could use that doesn't look too thick ? Thanks.