what does it mean when the battery light comes on

Your alternator has a problem, maybe the belt, it is not getting charged (the battery)

I had a battery light come on and the alternator was acting funny. Driving at night down a country road and suddenly the headlights became super bright and then dimmed to normal again. This happen ed sporadically for a month. Then just the battery light remained. The battery never went dead so I knew the alternator was charging. I ran into a kid who worked at Toyota who told me it was a bad battery.....but my truck started all the time. I assumed this was due to an overcharging condition and not good for battery but otherwise not harmful. I had a used alternator laying around and went to swap it. When I removed my alternator I found the plug had 3 wires broken off. Once the wires were repaired my light went off. This thing was still charging because I ran it that way for 9 months. The battery was NOT bad. Amazing.

It means that you must perform a diagnostic on your alternator. Check the wires and the alternator belt for wear and tear. There could be a diode malfunction within the alternator. If not tended too, you will eventually have an alternator dilemma. It happened to me. I changed the alternator and the light turned off.