Battery

[pps]

My battery dies while I'm driving on a 1990 535I. Please help.

[Tiger]

Charge up the battery and check it's condition... then check your charging system... It is most likely that your alternator is bad especially if your car is running on battery alone... Also check if your alternator belt is still there if not serpentine.

[Aaron Bakos]

My battery dies while I'm driving on a 1990 535I. Please help.

What's the output on the alternator?