Sounds like the brushes are worn down in the alternator.
Possible alternator problem
Battery light usually means alternator not charging. Most common solutions would be be a bad alternator, bad connection, or loose alt belt.
Clean both battery cables and check the connections on the alternator. If it continues, go to auto zone and have the alternator checked.
Yes
Clean the battery cables and make sure the wires to the alternator are tight and without corrosion.
A light may flicker due to a loose bulb, faulty wiring, a problem with the light switch, or a fluctuation in the electrical supply.
Might be a weak battery
If the battery light flickers, it's losing voltage. It would be worse when the lights and other accessories are running. It just may not be enough to kill it yet. I would suspect parts in this order. Alternator(if there is a voltage guage, should be around 13-14 volts) discharged battery
The warning light doesn't tell you how healthy the battery is, it tells you if there are any problems with the charging system. A flickering light means charging is intermittant for some reason, so it would be worth checking the alternator or voltage regulator, which might be on the way out. It's worth also checking that the warning light circuit and bulb are ok - if it lights up brightly and continuously when you switch the ignition on, then goes off when you start the engine, it's ok. Hope that helps.
Why would battery light come on then go off
It could
Most likely, the alternator is going out. It puts out more at higher RPM's, so it would charge more going down the road than it would at idle. Good Luck!!!