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I had my 6S' battery changed in Apple Store around a month ago. Went to Apple Store on black friday, I was told that the battery would arrive in early-December. Received an e-mail on Dec 12th, got the battery changed on the same day. Took around 3 hours.
 
I had my wife's 6s battery replaced at an authorized apple service place. It took about 1 1/2 hours. Good as new!
 
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