Instrument panel keeps displaying the battery, this happens off and on? Owners manual states charging system but with no other detail. Like several people I don't have a lot of money to take it in to dealer if I had more information of what may be causing the problem.
Use an inexpensive digital voltmeter to measure the battery voltage while the engine is running. This must be done while the problem is occurring. It must be between 13.75 and 14.75 volts. If it is low, suspect worn brushes in the generator. If that's what it appears to be, I'll look up what they used on 2004 models. On older ones from the 90s the brushes were attached to the voltage regulator and were real easy and inexpensive to replace. Ford had a fairly decent design in the 90s so they had to change it for newer models.