Many of you are worried about the long-term reliability of electric vehicle batteries. I know because you ask me all of the time. Among skeptics and prospective buyers alike, it’s one of the first things to come up: Will the battery last? Yet more and more data is showing that modern EV traction batteries just don’t fail in significant numbers. You don’t have to worry about them. It’s the damn 12-volts that’ll leave you stranded in the office parking lot.
Internal combustion drivers know that risk. Traditional cars use a 12-volt battery—usually a chunky lead-acid unit—to start the vehicle and power the electronics. You may expect that EVs, with their massive drive batteries, don’t need these ancient bricks.
Yet they rely on them for the exact same reasons. EV 12-volt batteries are used to switch on the primary power system, power low-voltage electronics like infotainment systems and operate background tasks like passive entry systems and cell connectivity. Just like on an internal combustion car, if they run out of juice, you may be stranded. Your fully charged, giant main battery won’t be able to help you.
You may have a $20,000 lithium-ion battery propelling you around town, but that whole experience likely still relies on a simple, $200 12-volt battery.
“I think there are just some misconceptions,” Steven Elek, senior automotive data analyst at Consumer Reports, told InsideEVs. “People are like, oh, it’s a rolling battery. My battery should never go dead. But that’s just not how they work.”
Issues with 12-volt batteries are clear in Consumer Reports‘ reliability data, Elek said. While the firm couldn’t confirm whether 12-volt problems are more common with EVs, it has data showing them as consistent trouble spots for EVs like the Hyundai Ioniq 5, Kia EV6, Rivian R1S and Rivian R1T. Forums for any of those brands support the issue.
Hyundai, Kia and Genesis have all had to recall EVs due to issues with the system that charges the 12-volt battery. Rivian, for its part, completely redesigned the way the 12-volt battery is maintained for the second-generation R1.
How EV 12-Volt Systems Work
To understand these issues, you have to understand how EVs charge and use their 12-volt batteries. They typically use what’s called a DC-to-DC converter. The system takes direct current (DC) from the main battery and steps it down from the pack’s voltage—usually anywhere from 300 to 900 volts—to the charging voltage of a 12-volt battery which is—confusingly—14 volts.
There are two basic strategies for how to manage this. Most companies use a simple approach—when the vehicle is on, the high voltage (HV) system charges the low-voltage (LV) 12-volt battery. When it’s off, there’s very little power demand, so the battery should last weeks without the vehicle powering on. That’s how it works in an internal combustion vehicle. Elek notes that for safety reasons, many manufacturers never want to engage the HV battery without the user choosing to start it.
A Bosch DC-to-DC converter.
Photo by: Bosch
Other designs use more power when switched off, and therefore have an automatic power control logic that will flip on the HV battery to top off the LV system when it gets low.
Why EV 12-Volt Batteries Fail
Rivian infamously used such a system on the original R1S and R1T lines, leading to what users call “vampire drain.” The car’s connectivity features and its security feature, gear guard, often deplete the 12-volt battery. When that happens, the whole HV system wakes up to feed the 12-volt, leading to the drive battery draining.
Countless consumers have complained on forums that their Rivian loses a significant amount of battery just sitting still. As this video from MotorSport Unplugged shows, the constant cycling on the 12-volt battery can lead to premature failure of the 12-volt battery itself. There’s a reason, too, why this may be more surprising and inconvenient than 12-volt failure in an internal-combustion car.
“I think the other thing that happens is, we as owners and drivers, we’re so conditioned to the fact that when you hear that slow crank on your internal combustion vehicle, instantly we know, oh, hey, my battery’s getting low, I need to get it checked, I need a new battery,” Michael Crossen, an automotive engineer at Consumer Reports, told InsideEVs. “You know, it’s winter, I don’t wanna get stranded, that you buy a battery. You’ll never get that in an EV.”
We’ve also seen designs that constantly feed power to the LV system from high-voltage battery. Those have issues, too. When Out Of Spec’s VinFast VF8 bricked itself in a parking lot, the drivers tried the ol’ IT department special. They tried to turn it on and off again. Disconnecting the 12-volt battery is usually the easiest way to force a car to do a full, hard reset. Yet the VinFast continued powering itself using the HV battery, meaning they couldn’t reset the system for the better part of a day.
Photo by: Patrick George
Rivian updated the R1T’s LV battery charging system as part of the Gen 2 refresh.
Yet the simpler route is not without its pitfalls. EVs from Hyundai, Kia and Genesis don’t have the same power management issue as Rivians. They have a much worse physical issue. The Integrated Charging Control Unit (ICCU) that charges the 12-volt batteries in these vehicles is a key failure point. A transistor within the unit can be damaged by overvoltage, making it unable to charge the vehicle’s 12-volt battery. When that happens, it’s a ticking clock until you lose all 12-volt power. That will lead to a gradual loss of drive power, which the recall notice notes could potentially increase the risk of crashing. Well, multiple recall notices.
Hyundai has been trying to fix this issue for years, with multiple recalls. We’re still seeing anecdotal reports of problems even among vehicles that have previously had recall work done on the ICCU. They’re not the only ones. VW had issues with the 12-volt batteries on the ID.3 (which isn’t sold here). Chevy had teething issues with the 12-volt system in the Bolt. Even Toyota—the paragon of reliability—didn’t get things right on its first try. A bZ4X left Out Of Spec’s Kyle Conner stranded due to a dead 12-volt battery.
Kyle Conner got stranded by the Toyota bZ4X’s 12-volt battery issue.
Is This A Long-Term Issues For EVs?
Time heals all things. That remains the case here. While older Tesla and GM EVs occasionally had issues with 12-volt batteries, yet newer models have been completely fine. Rivian’s newer R1 seems to have solved the issue with a trickle-charging approach that no longer energizes the entire car just to charge the 12-volt battery.
Here, we’re once again seeing a symptom of a greater trend in EV reliability: The problem isn’t EVs, it’s new designs. There’s nothing inherently wrong with a DC-to-DC charging system. Yet automakers that have decades of experience building alternators now have to work with a new system. Like any complicated part designed from the ground up, there’s a chance of having a design flaw.
Photo by: Hyundai
These correspond with a larger trend in the automotive world. The simple, decades-old 12-volt battery is being asked to do more and more. Modern vehicles have more screens, sensors, antennas and lights asking for power. Far more of these systems must also be at least partially available when the vehicle is off. Your car that can remote start via an app needs to keep its cellular modem energized constantly. Ditto its proximity key sensors that enable keyless unlock. Walk-up lighting also means that if you walk past your car to walk the dog, you may trigger its headlights. This happens to my Blazer EV constantly.
These issues are not EV-specific, and neither is the growing trend of starter battery issues.
“So actually, I mean it’s across the industry that the starter batteries have been kind of an issue for consumers,” Frank Hanley, senior director of automotive benchmarking at. J.D. Power, told InsideEVs. “It’s been a problem for EVs more so, but just in the industry in general it’s been a rising problem.
Photo by: Tesla
Tesla had some issues when it moved the Model 3 to a lithium-ion 12-volt battery, but those are in the rearview mirror. It does not appear that 12-volt issues are significant issue for modern Teslas.
The good news is that things are getting better. Automakers are getting more experienced not just with EV technology, but also managing the workload on 12-volt batteries. Some have moved towards dual-battery setups or, in the case of Tesla’s Cybertruck, a primarily 48-volt system.
Automakers are also getting more intentional about choosing low-voltage batteries better suited to EVs. Many are switching toward deep-cycle batteries, which are worse at handling the high-current demand of starting an internal combustion vehicle, but better suited to being depleted more often. Slowly, automakers are learning the hard lessons.
“It’s a learning curve. I mean anytime you introduce new technology and features, it takes a while to get right,” Hanley said. “This is one of the growing pain points we see with the electric vehicles.”
Contact the author: Mack.Hogan@insideevs.com.
