Awesome! Glad it worked. I'm no expert regarding the battery, but it should be okay. Lots of people use laptops as servers with them plugged in all the time. Just keep an eye on it and if you see any signs of swelling or excessive heat, pull and/or replace the battery.
On the Mac, open qbittorrent, select all torrents in the client, and export them as torrent files or magnets, whichever you prefer.
Copy all the torrent/magnet files to a thumb drive or something and copy them to the elementary laptop.
On the elementary laptop, start without an internet connection. Connect the external drive with all the downloaded files, mount it if elementary doesn't auto mount it, and note the path.
Open qbittorrent.
Set the default save path in qbittorrent to the path of the mounted drive with all of your downloaded files.
If you want to do it in bulk, now add all the torrent files to QBittorrent. You may have to verify the file location for the torrents to make sure it sees the files on the drive.
Once you're certain all the loaded torrents are pointing to the save path for the files, you can close qbittorrent, connect the laptop to the internet, and relaunch qbittorrent.
It should verify all the files it finds for the torrents, which can take some time if you have a lot of torrents, and once verified it'll automatically start seeding
For me it's Perl's rename, which of course cones in a variety of package names depending on the distro you use. In trying to find a link, I landed on this stack exchange answer that gives a great overview of how the tool works and the different packages available on different distros.
I have to bulk rename files every day, and using regex and the other features of Perl's rename makes it so much easier to do.
Happy to help!