Garmin repair crews?

I called Garmin to let them know that my battery in my 5 month old GPS was only lasting 20 minutes. They had e pack just the unit up and they would fix it. O.K. That is cool, so I sent it back. When I got it yesterday, everything I had in it was gone. Master reset I presumed. But I also noticed some other differences, It actually picked up a signal in my mobile home, it's never done that before, even on the sunniest days. (It's cloudy and raining now) I thought they must have found a few other problems? Like the volume now is LOUD.. Boots up a lot faster. Was my GPS a mess? Then I looked at the serial number. This wasn't my GPS, it had a different serial number. Oh well, I like this one better, no scratches real clean. And works better, what more can I ask for? I logged on Garmin's website and noticed they still had my old serial #, so I emailed them and they changed it on the site. This unit works better than mine did when it was new!!