Hello,
What normally you want to do is always have your battery checked first. The way the charging system works is like in a circle. If your battery light came on, it is normally only a few issues it could be.
Number one is battery is either not good connection, or more some bad cells and is not holding proper charge. At almost any auto store, like shucks, auto zone, and these little buildings you see around that specialize in only selling of batteries and alternators, will check your battery to see if is good for FREE!!
Number two, is these same auto parts stores can also put a meter on the system and check to see if alternator is putting out the power to charge the battery, and again, can do this for FREE!!
Number three is, first check to make sure your belts that are around your alternator are tight and not loose or warn, or missing of course. And make sure the connections from your battery via alternator and starter are all tight.
Conclusion: The battery could be bad, if bad cells, or the terminals are corroded which means not getting good connection to charge the battery, so first double check that, but then have it tested and that is the easy fast way to find out if battery is poor. If that is the case, just replace battery. If battery is good, and belts and connections seem good, then most likely it will be the alternator. And that is something that is easy to replace and do yourself with minimal tools. I hope this helps, and i am sure this will solve the problem for you. Thanks Mike, from fixya,