This is more of a why question than a How to.
One of my remotes was acting up this morning and after unlocking the car it decided not to work anymore. I used the spare to start the car and take my son to school and when I got back I checked the battery.
While doing this the spare remote stopped working as well. I have re-synchronised both and all seems good again.
But I'm just curious why this happened? Is there something that would normally cause this??