Help Please

[ALX5]

Yesterday something unusual happened to my 01 3.0 X5 78,895 miles. In the afternoon I needed to do something in my garage so I moved the x5 out then moved it back in half hour later. It was running great as usual. However, later in the night need to run to the store for my baby's stuff, the X5 would not start. It started first then shut off immediately then would not start at all later tries. All of the instrument lights are on and seem to get power but the car refused to start. I can hear the cliking sound of the alternator. I am thinking more of the battery but still not sure. May have to wait until get home from work today to give it a jump. Did anyone ever have this problem? any sugestion will be appreciate very much. Thanks

ALX5