The same thing happened on my 02. At first i thought it was my battery so I got it recharged it and everything was fine for like 30 mins. Then all my electronics started going crazy and my X5 went into some sort of safety mode. It wouldn't go past a certain speed. Then all my electronics shut off while the engine was running. Not even the speedometer was working. The engine ran for a good 5 to 10 minutes then it stalled. I was lucky my dad was following me since we were going to pick up some family members at the airport. After continous attemps at jump starting the car it finally started, but it would shut off at 10 minute intervals, even earlier when the rpms dropped. Needless to say, it was not a fun day. I recommend you get the alternator checked out since that was my problem. After that incident i lost faith in the OEM alternator and purchashed one from autozone with a lifetime warranty. The continuous jumpstarts also damaged the battery. So I got a battery there too, with a lifetime warranty. Switched them out for 100 labor (altogether) and $ 350 in parts.