I downloaded Battlefield 3 with all the expansions to my laptop from a friend's house (he has internet speeds of 300mb). When I got home I wanted to copy the files to my desktop PC, and just replace the files in the Origin game download like it was before.
I followed these steps:
Start the download
Replace downloaded files with full game files
Restart the download
Origin only detected approx 65% of the files and left me with 8GB to download. Am I doing something wrong? I've read forums about how to backup games in Origin and it's all the same.
Don't place the files mid-download. Start the download as if you had no files at all, Origin will recognize as much as it's able to. If you still need to download extra files, there's nothing much you can do but wait for those files to download.
As Origin does not have a proper backup method, users have come up with this but it's not foolproof at all.