My Laguna Key cards?

Hi, I have a y/51 plate laguna. The key cards have been working fine untill recently. They have both stopped working completely. They are not unlocking the car atall. At first I thought the battery on my one may need replaced but the spare key is doing exactly the same thing. I doubt this is just coincidence that they both need new batteries. Does anyone know what the problem may be?

Thanks

Emma
August 2009