Don't worry!
I have had this problem. More than likely the rubber stopper on your brake pedal is worn or missing. Go out to your car and follow the metal on your brake pedal up until you find a rubber stopper or piece of metal with a hole in it. The rubber stopper hits a sensor when you brake pedal is not being pressed. This sensor tells the brake lights you are not pressing your brake pedal. If it is worn or missing it will not hit this sensor and the brake lights will stay on, which can cause your battery to die!!
Let me know if this helps!!!