We often hear about Auxiliary batteries, especially in EVs. Although an auxiliary battery is also present in ICE vehicles, we call it a battery rather than an auxiliary battery.
We call it an Auxiliary battery in EVs because it is an additional battery on top of the main traction battery that is used for powering the motor.
Let’s learn more about What Is An auxiliary Battery, how it functions, and what is the Difference Between Auxiliary Battery And Traction Battery here in this article.
What Is An auxiliary Battery?
An auxiliary battery is a small battery used in EVs to power various supplementary equipment, such as the lights, music system, navigation, and other similar functions.
Only the air conditioner is run by the main traction motor. All other secondary equipment is powered by an auxiliary battery.
We don’t have to charge the auxiliary battery as it will be auto-charged when the motor runs. This is similar to how an IC engine vehicle charges its battery.
In an IC engine vehicle, there is one more battery, a starter battery, which is used to start the engine.
Typically, an auxiliary battery is small in size and capacity, around 12V. It is placed under the hood or trunk or in similar places in a car.
Auxiliary batteries are typically lead-acid batteries, but some manufacturers, like Tesla, are also switching to lithium-ion for the auxiliary battery.
What Is A Traction Battery?
EV batteries, also called traction batteries, are large in size and capacity. Their capacity is rated in kWh. The more kWh the battery has, the better its range.
Unlike an auxiliary battery, a traction battery stores energy and runs the motor when needed. Multiple battery cells are contained in a container called a battery pack.
Traction batteries are mostly lithium-ion batteries. Lithium-ion batteries are known for high energy density. This means you can get a high kWh battery pack in a small box, which is ideal for EVs
A traction battery runs the motor and charges the auxiliary battery. It is also used to run heavy equipment like the air conditioner and the heater.
The traction battery voltage depends on the number of battery cells contained in the battery pack and how much voltage they carry.
For example, if a battery pack has 50 battery cells and each cell carries 2 volts, then the battery pack voltage will be 100V. Typically, an electric car EV battery voltage will be more than 300V.
Difference Between Auxiliary Battery And Traction Battery
Here are some differences between an auxiliary battery and a Traction battery.
| Auxiliary Battery | Traction Battery |
|---|---|
| The traction battery charges the auxiliary battery when the motor runs | For charging, you need an external charger |
| Small in size | Big in size |
| Small in capacity | High on capacity |
| Typically lead-acid battery | Typically lithium-ion battery |
| The voltage is around 12V | The voltage is more than 300V ( For cars) |
| Very short life | Very long life |
| Cheap price tag | Extremely costly (Almost 50% of the vehicle cost) |
FAQ: What Is An Auxiliary Battery
What Does The Auxiliary Battery Do?
Auxiliary batteries in cars run supplementary devices such as lights, music systems, navigation devices, etc. Due to their high power requirement, they can not run the AC in cars.
