More than likely your alternate is failing.
Check your battery. And have your alternator checked. Most auto parts stores will do it for free.
Why would battery light come on then go off
If it is undercharging the battery yes, but if it is overcharging the battery no in most instances. If it fails completely the light will come on.
what causes the battery light to on a 2005 ford expedition to come on?
Battery
It could
Disconnect the battery cable, wait few second that reconnect. That will reset the engine light but doesn't fix the problem. if the problem was not fixed the light will come back on.
More than likely the alternator is defective. Have it tested at most auto parts stores.
Your battery is probably dying
Disconnect the negative battery cable for about two minutes. Know that if you do not repair the problem that set the light in the first place it will just come back on.
A bad stator causes the battery not to charge. That makes the battery light come on. Some other things that can cause the battery light to come on are corroded or frayed cables or connections or a loose/bad ground cable.
NO! where does the power (voltage and current) come from if the battery is flat/dead?