After almost 2 years my iPhone 6s battery was worn out. I got a little bit over 2h on screen time looping YouTube videos and during the night the battery was drained by 30-40% with screen off. Since I did not want to upgrade yet, mainly because iPhone 6s is still very capable phone and I did not see anything groundbreaking on the market, I decided to give a try changing a battery.
Finding battery was not hard. Mainly there are 2 options- China parts from ebay which can be good and can be total waste of money, or iFixit which claims that their parts are top quality.
I decided to go with iFixit since they provide all the necessary tools as well for good price. Changing battery was pretty straight forward with provided guide. It took me around 30 minutes to swap batteries.
I did recommended calibration- discharged phone till it shuts down, then charged to 100% interrupted. Then I run youtube on auto-looping to see how long the new battery will last.
On tests I found on youtube, new original battery lasts around 5.5 hours. But since I have a different version of YouTube app and different version of iOS (I have installed iOS 11 developers beta) my results can not be directly compared because too many things are different, they are rather just number what you can expect.
So during the night my phone in stand by mode decreased by 0% (might be calibration issue) and running YouTube loop I got a little bit more than 4 hours of screen time which is a great improvement. The biggest mystery is whether this time is because