Do I need a new battery?

you could have a bad ground or a short somewhere. or could be something in your ignition... is the stereo stock or has it been changed. if it has been changed in behind there would be a good place to start looking for your short as most radios are turned on and off by ignition but the memory wire is usually a low current signal powered by the ecm. I would start by cleaning the terminals on your battery and using either dialectic grease or vasoline to keep from corroding. if it were your battery if would not want to start the next day or barely start. if you would like to test your battery napa should do it on site without any cost. (double check though)