What exactly is the problem? Car won't open or won't lock?
If it's a flat battery you should definitely get a warning on the dash. This is fairly standard for cars with some form of keyless entry or keyless ignition as the batteries tend to drain far quicker than a conventional key fob. My Focus had it 7 years ago, so don't accept any dealer baloney about a warning being an option. If you use the search function on here you'll see others have had warnings when the battery is getting low, the batteries tend to last about 12 to 18 months if you have keyless.
In my experience these systems can be temperamental, the central locking on my Focus would occasionally freeze and refuse to unlock. Changing the battery in the fob made no difference whatsoever. Eventually resorted to opening the car using the key blade. Locked it again then came back to the car a couple of hours later and all was well again. Either just a glitch or opening the car manually has done some kind of reset 
Have you tried both fobs?
Thanks for the response Guzzle.
On the first occasion I couldn't unlock the car, second occasion I couldn't lock it and dashboard said 'key not detected'. Both times a new battery immediately resolved the issue. VW diagnostic both times have indicated the battery was low and despite me quoting from this forum where others have mentioned the 'warning notification' the garage is saying there is nothing in the spec or in their knowledge to indicate that displaying a notification is an option.
When I picked it up tonight they suggested it was a rubbish battery causing it to stop working. I don't have a problem with the battery not lasting, I'll get spares, but I would quite like to be warned of the fact.
Apparently they are now going to ring the factory with my chassis number to check whether a notification option should appear.....so after 2 trips hopefully they will accept there is a problem and start thinking how it can be fixed!
Least they didn't wash it
