Oh no more woes -- If you 'd like to swap back to the older shape new shape Laguna for about two years ( ho hum ) then I'll gladly see if I can eventually sus the problem out for you..
In all seriousness I presume the battery on the hands free card gets more use as it has to remain active ?
When new what was the range ? Is this adjustable ? Do you leave your card key close to the car at any point during it's daily life ?