Should NOT need to be resynched... There is something else going on with your remote. Did you somehow soak it in water? How old was then "new" battery? .. I now know that if the fob is dead, you can place it against the steering column where the key WOULD go and the car should start. ...
I was having problems with one of my remotes after running it through the wash for the second time, and now keep a spare battery in the glove box along with an instrument screw driver for prying open the remote. (I have since obtained another remote, since the washed one will only keep a battery for 2 weeks). ...