Yeah as mentioned above, it is possible that your alternator is bad, you can get it checked while it is still in the car, take it to a place like Auto Zone and they will check the alternator, battery and the starter for free. Also from my experience when a battery starts to go bad (I suspect this is your problem) it will make the alternator work harder and in short notice you have a bad alternator. Make sure to check all of your connections and the battery terminals as they could be corroded and might need cleaning (makes better contact).
Good luck!!
