Any methods to test if the electrical system is working properly? Tests such as making sure the alternator is charging the battery? Something draining the battery when not in use? I've made sure all the lights are off after parking.

I just got a new battery 3 months ago and today, the battery was dead. Although I've only driven the car 700 miles in the last 3 months, I wouldn't think a battery should drain that fast. I've had the car in the garage for 3 weeks straight untouched and it started perfectly without any hesitation.

Thoughts?