I was driving the on the highway and I got the message "charging system failure" Is this the Alternator or Battery. I phoned the shop I usually deal with and they said they would have to do a diagnostic to be able to tell the problem but they said it was more than likely the Alternator. If it is the Alternator how easy is it to switch it out and how long will it take approx. Does anyone have any instructions on how to do this? Any help would be much appreciated. 2004 Grand Prix with 180,000 kms