Have you ever woken up to a drained battery even if you didn't leave your headlights on overnight? It's a common issue, and one that could be related to a number of problems with the battery. It's possible that there is a leak or a problem with the alternators, for example.
However, it's also possible that the battery terminals are simply dirty, according to HowToCleanStuff.com. These terminals get corroded as grime and dirt builds up inside a vehicle, and that can ultimately cause problems with your power supply.
Fortunately, this problem is easy to diagnose and clean. You should see a white deposit around the base of your battery if the corrosion is an issue. If so, detach the cables to your battery (negative first, then positive), take some baking soda, and pour it onto the terminals. Then, using a toothbrush and some water, scrub the battery posts until they're clean. Some automotive parts stores also sell specialty devices that cleans this part of the battery.
If this doesn't fix the problem, it's possible that things go deeper than simply dirty battery terminals. Taking the vehicle into a certified mechanic for vehicle inspections or diagnostics can be helpful in determining what exactly is wrong with the car.