Hello!
From the description of the symptoms, it does sound as if your car is not charging. You can find out if it is charging or not by using a voltmeter connected between the battery terminals. If it is charging normally, you should be measuring between 13.5 and 15 volts.
If you do not ahve a voltmeter, most auto parts stores and many repair shops can easily check this for you for free out in the parking lot if the car will drive there. If you cannot drive teh car that far, most auto parts stores can bench test the alternator for you if you remove it and take it there.
When a Subaru stops charging, 99.9% of the time it is due to a faulty alternator.
I hope this is helpful; if this answers your question then please click the ACCEPT button to close the question. Thanks!