The battery is one of the simpler components of your automobile, but it is also one of the most important. A battery that is weak or has gone dead cannot provide the energy needed to engage the car's starter and get the engine moving. Occasionally, an automobile battery will drain overnight, leaving your car inoperable in the morning.
The battery may be old, weak and unable to hold a charge. The battery will have a label on it stating the warranty period, which is how long you should expect the battery to last. If you are nearing or exceeding the warranty period, you should replace the battery.
Accessories can significantly drain a battery overnight. Check to make sure you didn't leave any accessories on overnight, such as the headlights or internal lights, which can drain the battery. Also, make sure you unplug any accessories, such as cell phone chargers or DVD players, from the vehicle when you park it.
There may be an issue with the vehicle's charging system. If you have a weak alternator, the battery may not be charging properly while you're driving. Some auto parts stores will test your charging system for free. If you can start your car with a jump start, you can take it to an auto parts store and they can test both the charging system and your battery to help pinpoint the problem.
An electrical component in the vehicle may be draining the battery while the vehicle is off. This can be caused by a relay that is stuck in the "on" position.