What does your EV have in common with an aircraft?

It’s all about the batteries. Or more to the point, using different batteries for different jobs.

You see, aircraft are designed with separate electrical systems supported by separate batteries. That’s because critical safety functions should never rely on one source of power alone.

Your EV works on a similar principle.

While the large high-voltage battery provides the energy that powers your car’s motor, a separate 12-volt battery supports the car’s computers, safety systems, controls and everyday electrical functions.

It’s a much smaller battery, but it plays a critical role every time you unlock, start and drive your EV.

Why is a 12-volt battery so important? 

An EV’s large high-voltage battery is principally used for powering the motor. But it doesn’t run every system in the vehicle.

That’s where the 12-volt battery gets busy. It helps wake the vehicle up, it powers the computers and control units that check the car, it activates its electrical systems, and it safely connects the high-voltage battery.

In simple terms, the large battery moves the car. The 12-volt battery helps the car operate almost everything else. If your 12-volt battery is flat or failing, your EV might not unlock, start or move – even when the main battery’s fully charged.

An aircraft-style approach to electrical safety

Modern aircraft are built with redundancy in mind. That means important systems are separated so one electrical issue doesn’t automatically shut down everything else.
Electric vehicles do a similar thing, using separate high-voltage and low-voltage electrical systems.

The 12-volt battery isn’t simply old technology carried over from petrol and diesel vehicles. It remains an important part of the way modern EVs are designed to operate safely and reliably.

It supports all the low-voltage systems that control, monitor and manage many of the vehicle’s essential functions such as:

• vehicle computers and control units
• central locking and security systems
• dashboard displays and warning lights
• interior and exterior lighting
• cameras and parking sensors
• infotainment and communication systems
• climate-control electronics
• the systems used to activate the main EV battery
• Advanced Driver Assistance Systems (ADAS)

The battery might be small compared with the main EV battery, but the number of systems relying on it can be significant.

Why the 12-volt battery matters for ADAS

Just about all EV’s are fitted with Advanced Driver Assistance Systems, usually known as ADAS. These systems include all the clever safety stuff in your car like:

• autonomous emergency braking
• forward-collision warnings
• adaptive cruise control
• lane-departure warnings
• lane-keeping assistance
• blind-spot monitoring
• driver-monitoring systems
• reversing cameras and parking sensors

This ADAS technology relies on cameras, sensors, computers and control units working together. And they all need a stable and reliable low-voltage power supply.

In other words, a healthy 12-volt battery to support your EV’s safety features. A weak battery will not only compromise ADAS, it can sometimes contribute to warning
lights, electronic faults or systems behaving differently from normal.

Which is why battery testing is about more than just checking to see if your vehicle will start or not. It’s also about helping maintain the systems responsible for safety, control and driver assistance.

Comfort and convenience also depend on it

The 12-volt battery also supports many of the convenient features you use every day to make driving more comfortable. Things like:

• door locks
• electric windows
• screens and displays
• cabin lighting
• audio systems
• communications
• charging controls
• climate-control electronics

As you can see, as vehicles become more advanced, the electrical demand placed on the 12-volt battery continues to increase.

Can an EV have a full battery and still not start?

Absolutely. Your EV might show plenty of range in its main battery, but it can still be unable to unlock, wake up or drive if the 12-volt battery is flat.

This happens because the low-voltage battery is needed to power the vehicle’s computers and start the process that connects the high-voltage system. Without enough 12-volt power, the car may be unable to complete that process. So a small battery can cause a very big problem.

How long does an EV 12-volt battery last? 

Battery life varies depending on the vehicle, battery type, temperature, driving habits, charging patterns and how often the vehicle is used.

But as a general rule of thumb, many automotive 12-volt batteries need replacing at around five years. Some fail earlier, while others last longer.

The difficulty is that battery deterioration can happen gradually. The battery might appear to be working normally until the vehicle suddenly fails to start or begins showing electrical warning messages.

Regular battery testing is the best way to understand its condition before it fails.

What are the signs of a failing EV 12-volt battery?

Possible signs include:

• the vehicle is slow to wake up
• the doors don’t unlock normally
• the vehicle won’t start
• dashboard warnings appear unexpectedly
• lights or displays behave unusually
• electronic systems work intermittently
• the vehicle has been parked for an extended period
• the battery is approaching four or five years old
• you don’t know when the battery was last tested or replaced

These symptoms can have several causes, but the 12-volt battery is one of the first and simplest things to check.

Free battery testing at Battery Town

Don’t wait until your EV won’t start. Battery Town offers free 12-volt battery testing at locations right across New Zealand. Just pop in and we can:

• test the condition of your EV’s 12-volt battery
• check whether it’s holding charge properly
• assess its ability to deliver reliable power
• identify the correct replacement battery if required
• make sure the replacement suits your vehicle.

Not every EV takes the same battery. They vary between makes and models, so fitting the right battery is super important.

At Battery Town, we’ve got the specialised testing equipment, battery knowledge and product range to make sure you drive away with the right battery.

Frequently asked questions

Do all electric vehicles have a 12-volt battery?
Most electric vehicles use a separate low-voltage battery alongside the large high-voltage battery that powers the motor.

Why does an EV need a 12-volt battery?
The 12-volt battery helps power vehicle computers, controls, lighting, central locking, displays, safety systems and the process used to activate the main battery.

Can a flat 12-volt battery stop an EV?
Yes. An EV can have a fully charged main battery but still be unable to unlock, start or drive if the 12-volt battery is flat.

How long does an EV 12-volt battery last?
Many 12-volt batteries last around five years, but battery life depends on the vehicle, battery type, climate and how the vehicle is used.

Does the 12-volt battery support ADAS?
Yes. The low-voltage electrical system helps support the computers, sensors and control units used by many driver-assistance and safety systems.

Where can I get my EV 12-volt battery tested?
Battery Town provides free 12-volt battery testing at locations across New Zealand.