Start the Origin client and go trough all activation steps that consist of entering the Product Key. If the computer is offline and can not reach origin activation servers, it will report that it can not validate the key, but it will enable you to continue. Confirm that message and wait up until the origin goes into the profile choice or production screen.
Exit the game.
Locate file activation.scb stored in Documents -> Battlefield 1. The file contains the encoded Product Key which you have previously entered, plus a unique checksum number generated from user id of your Windows profile. There are no private data in this file, no name, no e-mail, nothing to identify you personally.
Copy the activation.scb file on a USB memory stick or use any similar means to transfer the file to another computer connected to the Internet.
Wait until the activation process finishes. It might take up to a minute. Please wait till this page updates itself to show you the outcome of the operation. It will direct you through the rest of the process..