There’s no denying that the rapid advancement of technology has inspired car makers to push beyond the parameters of what a car can do.
Despite numerous high-tech features like autonomous emergency braking and lane keep/assist becoming the new normal in cars sold today, the humble 12V battery is still one of the most crucial components in most new petrol/diesel, hybrids and electric cars sold in Australia today.
But why is this battery so important to most cars in 2025? Here’s what you need to know.
What does the 12V battery in your car actually power?
Depending on the type of car, experts said the 12-volt battery is crucial in powering numerous electronic features.
In the case of internal combustion engine (ICE) models, David Thomson, Team Leader of Technical Services at the Victorian Automotive Chamber of Commerce (VACC), explained “In ICE models, the 12V battery powers all electronic control units (ECU) and electrical accessories throughout the vehicle.
“When the ignition is turned on, these systems are energised first. Then, when starting the engine, the 12V battery provides the high current required for the starter motor to rotate the crankshaft, which then starts the engine,” Thomson told Drive.
For electric and hybrid models, the 12V battery powers other car features as well as providing critical support for the car’s main high-voltage battery.
According to Stuart Charity, the CEO of the Australian Automotive Aftermarket Association (AAAA) – a national industry body with members throughout the entire maintenance chain – the 12V battery found in new EVs and hybrids “powers the car’s low-voltage systems and electronics” such as computers, lighting, wipers, climate controls, power windows, alarms, locks and infotainment system.
Why does an EV have a 12V battery?
In electric vehicles – where a high-voltage battery typically propels the car – Thomson said “the 12V battery is crucial” as it is a part of the car's charging function.
“It energises the HV [high voltage] contactors that connect/disconnect the HV battery, supports the inverter logic that converts high-voltage DC to motor-driving AC, and is required to initialise charging when the vehicle is connected to a charging outlet.
“Without a functional 12V system, the high-voltage battery cannot be engaged or charged,” Thomson told Drive.
Additionally, Charity explained that the small battery found in EVs is an important safeguard that protects people from getting electrocuted.
“Its most important function, though, is safety-related. The 12V battery is responsible for coupling and decoupling the high-voltage battery via the main isolators as part of the start-up/shutdown procedure or in the event of an accident to avoid electrocution,” Charity told Drive.
The common reasons why a 12-volt battery fails
Generally speaking, 12-volt batteries in most cars fail due to the general wear and tear caused by years of consistent use.
As Thomson pointed out, “Modern vehicles place a constant strain on the 12V system, even when the car is parked [due to the car’s] sensors, control modules and monitoring systems slowly drawing power. If a car isn’t driven often enough, the battery can gradually discharge and deteriorate.
“Over time, these repeated deep discharge cycles can shorten the battery’s lifespan and reduce its ability to hold a charge,” he explained.
Similar to petrol/diesel-powered cars, Charity from the AAAA said an EV’s battery can be impacted “by general age, wear and tear, as well as vehicle faults that cause a constant (parasitic) current draw that causes rapid battery failure”.
Additionally, the CEO of the AAA told Drive, “Unlike the high starting current in ICE cars, 12V batteries in EVs typically don’t experience the powerful, deep discharges and subsequent recharges that help break down deposits on their plates.
“This leads to a gradual reduction in their ability to store charge. Some EVs are also programmed to reduce or stop charging the 12V battery when the main high-voltage battery is low.
“Software glitches can also occur and can prevent proper charging or cause excessive discharge of the 12V battery,” Charity explained.
What are the warning signs that a 12-volt car battery is starting to fail?
Generally speaking, most new cars have a dedicated battery warning light that alerts drivers that the car’s 12V battery is having some problems. Depending on the car, some telltale signs could also notify owners that the system is starting to fail.
In the case of ICE vehicles, Thomson from the VACC explained that “one of the easiest warning signs of a 12V battery starting to fail is a slower cranking speed when starting the engine. The starter motor draws significant current, so any reduction in battery capacity is quickly noticeable”.
However, the technical lead did acknowledge that a deteriorating 12V battery in EVs and in some hybrids “can be trickier [to identify] because there is no traditional starter motor and no obvious cranking speed to observe.
“As a result, the 12V battery issues often show little or no visible symptoms until the battery is severely discharged. Subtle signs may include slower responses from accessories, delayed infotainment start-up or error messages related to vehicle electronics,” Thomson told Drive.
Meanwhile, Charity from the AAAA said that “In some EV models, a failing 12V battery can prevent the car from being able to shift into gear or drive at all. The vehicle may take longer than usual to power on, indicating a weak battery”.
How to maintain and prolong your car's 12V battery
While battery deterioration is inevitable, experts say there are numerous methods for maintaining and prolonging your car's 12V battery.
The first and simplest is driving the car regularly, so the car's system can recharge the battery and maintain peak capacity.
According to Thomson at the VACC, for petrol/diesel cars “it takes approximately 20 minutes of run time for the vehicle's charging system to replace the charge taken out from a single engine start.
“If the car is used for only small trips of under 20 minutes, the charging system may never get the chance to replenish the charge back into the battery. This will eventually result in a no-start situation.
“Even in EVs and hybrids, regular use helps prevent slow discharge and keeps the battery in good condition, as charging the 12V system can often rely on the HV battery level and the vehicle being in the ‘Run’ or ‘Ready’ position. If the HV battery level is not high enough, the 12V battery will not be charged,” he told Drive.
Charity from the AAAA agreed and added “To maintain your EV or hybrid 12V battery ... minimise extreme temperatures by parking in the shade or garage, as heat degrades the battery.
“Regular servicing to test the battery's voltage and condition can help identify and address potential issues before they lead to a dead battery.”
Additionally, things like making sure the battery is clean, dry, and free of grime, as well as checking the nuts and bolts for any corrosion, can help prolong its life.
Ethan Cardinal graduated with a Journalism degree in 2020 from La Trobe University and has been working in the fashion industry as a freelance writer prior to joining Drive in 2023. Ethan greatly enjoys investigating and reporting on the cross sections between automotive, lifestyle and culture. Ethan relishes the opportunity to explore how deep cars are intertwined within different industries and how they could affect both casual readers and car enthusiasts.
