My buddy is trying to restore his sprint iphone 5s since he is having battery problems. He has always done OTA firmware updates so he wants to try a fresh restore. He has gone to this website to get the ipsw file. http://www.felixbruns.de/iPod/firmware/ He chooses this file for his sprint iphone 5s 8.1.1 (5s GSM+CDMA): iPhone6,2_8.1.1_12B435_Restore.ipsw However, when it tries to do a restore on his Windows itunes he gets the following message. "The firmware is not compatible." What is he doing wrong or what file should he be using?