WARNING!: You should NOT reconnect your battery FPC cable / connector until the VERY LAST reassembly step! Modify your reassembly procedure to move this "re-connection" of the battery connector until very last. I can't stress this enough. My logic board is now burned (it smoked upon reconnecting the LCD replacement part, because the battery was already reconnected and "live". The problem is that if you don't have the FPC connector aligned just perfect to the header (on the logic board), you create a momentary short (when the pins aren't aligned well)... this causes the Logic board to instantly burn. Save yourself trouble.
###You have been warned###
SERIOUS WARNING!: During *reassembly*, you should NOT reconnect the battery connector until the VERY LAST step (upon reassembly!), as many people, including myself, apparently have smoked (burned, destroyed) the main Logic board. This happens when you reconnect the LCD/digitizer assembly FPC cable. ifixit should modify this instruction to be very explicit about this!