If the battery is dieing from just SITTING, you likely have a short somewhere. If the battery dies after some driving and can sit relatively ok, your alternator/charging system is malfunctioning. Do this, get a battery charger for your car, charge the battery, and when it's done measure/record the voltage when the battery is disconnected from the car and connected to the car. Then turn the car on (that is engine running) and measure/record the voltage again. Tell us what numbers you read and we can have a pretty good idea of what's going on. If voltage drops when the battery is connected to the car you have a short. If voltage drops only between battery connected and engine on, your charging system is shot. Good luck and let us know!