The Chevrolet HHR (Heritage High Roof) is a compact car that was produced from 2006 to 2011. Some models of the HHR were equipped with two batteries, which served different functions.

The primary battery, also known as the starting battery, is used to start the engine and provide power to the electrical system when the car is running. The secondary battery, also known as the auxiliary battery, is used to power the car’s accessories, such as the radio, headlights, and power windows, when the engine is not running.

There are several reasons why the HHR was equipped with two batteries:

1. Improved reliability: Having two batteries allows the car to continue functioning if one battery fails. This can be especially useful in emergency situations, such as a dead starting battery, which could prevent the car from starting.
2. Increased electrical load: The HHR was equipped with a number of electrical features, such as power windows and a radio, which can drain the battery when the engine is not running. Having a secondary battery dedicated to powering these features can help extend the life of the primary battery.
3. Enhanced safety features: The HHR was equipped with a number of safety features, such as airbags and electronic stability control, which require a reliable source of power. Having a secondary battery dedicated to these features can help ensure that they function properly in the event of a power loss.

In conclusion, the Chevrolet HHR was equipped with two batteries to improve reliability, increase the electrical load, and enhance safety features. The primary battery was used to start the engine and provide power to the electrical system when the car was running, while the secondary battery was used to power the car’s accessories when the engine was not running.