Extremely hot or cold temperatures can have a significant impact on your car battery's performance. Generally speaking, hot temperatures will result in water inside of the battery being lost, and over time, it will lose the ability to create the chemical reactions needed to provide power to your vehicle.
If your battery is not sealed, it may be possible to pour water into it to extend the products useful life. However, most batteries are sealed, which means that once moisture is lost, it cannot be replaced. During the colder months, chemicals inside of the battery wont react as quickly, and this means that it takes more effort to start the car.
While newer batteries may be able to overcome this challenge, older ones are more likely to succumb to the harsh weather. Leaving a battery on a charger overnight may make it easier to start your car in the morning.