Volkswagen Passat Starter Motor Problems

I have had a problem starting my passat,it starts and then cuts out, if I wait 20 seconds and try again it will start no problem. I have had it in a garage and they have said it looks like it is losing a signal from the key to the immobilis...

when starting engine very slow turning over. never not started yet. had battery checked ok only thing i can think of is starter motor on way out, any idea,s thanks jontyB

The other day, I went to start the car but the battery was totally dead. So I got a jump lead start and its been alright since. It has happened a couple of times before but once charged it can be ok for weeks. Can someone help please.