Key fob batteries

Hi,

I have an Ulysse 2.2jtd 2003. I have just been advised that a message has appeared on the rt3 unit stating Immobiliser faulty. This has now disappeared and the car has started normally. I have read all the threads regarding this especially the ones about the fuse box in the engine compartment and two weeks ago I did, with difficulty remove the cover and check for water as my rt3 display appeared to have lines all over it, seems fine now. I could not see any evidence of water penetration. The other thought is, if the battery in the key fob runs down (mine are over 4.5 years old) can this effect the starting of the car or does it not have anything to do with it. If I do change the batteries is it just a case of opening the fob up and changing the batteries or is there more to it?

Thanks

Lou