All manufacturers say their engines will start with a good, fully-charged battery after sitting for three weeks. Most cars last a little longer. To be safe for six weeks there will be a cable to unplug or a fuse to pull. There shouldn't be a problem disconnecting the battery on a '99 model, but on many newer cars there are computers and radio that will lock up and some cars will not start or run above idle speed without a tow to the dealership and lots of money, ... Just from disconnecting the battery or letting it run dead.
You might want to disconnect the battery at home first for a few hours, then reconnect it and make sure everything works. If it does, you won't have to worry about doing that at the airport. Also, if you do not disconnect it at the airport, my guess is they will have a battery jumper pack to borrow because they've surely run into dead batteries before.