What Is The Purpose Of The 12-Volt Battery In An EV?

Quick Links

• 12V Battery Vs. High-Voltage Battery

• 12V Battery Uses In An EV

• Why Can't The High-Voltage Battery Be Used In Place Of A 12V One?

• How A 12V EV Battery Is Charged

• Types Of 12V Batteries

• What Happens If An EV's 12V Battery Dies?

Electric vehicles (EVs) utilize high energy batteries that are capable of putting out over 700 volts! These batteries provide the electrical energy needed by the electric motors that power the car. The high-voltage batteries (HVs) are charged from regenerative braking and at charging stations. With so much battery power, then, one may wonder what the purpose of a 12-volt battery in an EV is. 12V batteries are used in conventionally powered cars to start the engine. In this guide, we'll look at the slightly different role they play in an EV.

Testing-A-Car-Battery-With-A-Multimeter

Related

How To Test A Car Battery With A Multimeter

This simple test allows you to check the health of your car's battery.

12V Battery Vs. High-Voltage Battery

Firstly, let’s get into exactly what the difference between these batteries are. A 12-volt battery consists of six 2.1-volt cells totaling up to a maximum output of 12.6 volts (V). The 12V battery is found in vehicles with internal combustion engines. The battery stores electrical energy, powers the starter motor, supplies electricity to electrical circuits while the engine is off, and absorbs current spikes from the alternator.

The HV battery can have over 329 cells each generating 2.4V with a total output of about 800V.

The latest high-voltage batteries can output as much as 1,000V.

This means that HV batteries are much larger and much more powerful than a 12V battery. These batteries have to be large to power the electrical motors, but to also store enough energy to retain a decent range between recharges.

The EV1 from General Motors used 27 12V batteries; 26 were used for propulsion, totaling 327V, and one was used as an accessory battery. The EV1 only had a max travel range of around 60 and 100 miles; this was due to the limited battery technology at that time, resulting in inefficient battery cells. Today, high-voltage EV batteries have an average range of 260 to 400 miles. Not only are these HV batteries capable of storing more energy for longer ranges, this energy is responsible for making them very fast.

12V Battery Uses In An EV

It may not have an engine to start, but the 12V battery in an EV still performs a range of important functions:

• Powers the vehicles 12-volt electrical lighting systems.
• Powers the 12-volt audio, telematics, driver information system, and A/C controls.
• Provides the electrical energy needed to start the high-voltage system.
• Acts as a cushion or buffer for the HV system.
• Powers the diagnostic system for the HV system.

It is especially important for the vehicle to self-monitor faults and for repair facilities to understand where and why a malfunction is taking place. The 12V battery is crucial for this function.

Tesla 12V battery

Why Can't The High-Voltage Battery Be Used In Place Of A 12V One?

The HV battery is designed to handle large current draws and power the electric motors that move the vehicle. The HV battery is not designed to provide continuous electrical support for the vehicle’s electrical system. Adding more electrical loads and powering more systems would inhibit the full function of the HV battery. This would also require the HV battery to be much larger and heavier than it currently is.

Tesla HV battery

How A 12V EV Battery Is Charged

Because an EV 12V battery is responsible for handling the electrical systems of an EV, maintaining the 12V battery charge level is crucial to system operation and battery life. The 12V battery is charged from the HV battery. Battery temperature, charge, and output are regulated by a control module. The control module can allow the HV battery to slowly charge the 12V battery by a process called ‘trickle charging’.

Trickle Charging

Trickle charging is a slow charging process that uses a low amount of voltage and current. This replenishes or charges the battery at a rate equal to its discharge rate. In other words, the trickle charging process negates the discharge/depletion rate of the battery.

Why Trickle Charge?

The reason why the HV battery only trickle charges the 12-Volt battery is to extend both the life of both batteries. This is achieved by matching the charge/discharge rates but also by maintaining the battery’s temperature.

google news icon large

Add CarBuzz to your Google News feed.

Follow On

Google News

Types Of 12V Batteries

There are various types of 12V batteries, with some vehicles requiring a specific type.

The small 12V battery found in EVs is a deep-cycle battery.

What Happens If An EV's 12V Battery Dies?

As we covered above, the 12V battery is pretty important for an EV. If the 12V battery dies, the vehicle will not be able to power up the greater electrical system, including the HV battery control module. This will result in the vehicle being unable to move.

If the 12V battery dies, you can likely jump-start the battery like you would on a conventional car. Most EVs have dedicated ‘jump start’ terminals if the 12V battery cannot be easily accessed. In some instances, when the battery discharges too quickly or is incapable of holding a charge, the vehicle may need to be towed to a shop and the 12V battery will need to be replaced.

Another aspect to note is the different placement of a 12V battery in an EV. In the case of the Tesla Model 3, it's found behind the frunk under the hood. However, replacing it will also require lifting the rear-seat cushion to gain access to the low-voltage connector.

Close

N/A

Related

How to Jump Start a Car

How to get going again if your battery has let you down