The idea of a “12V battery reset” button strikes me as odd. Hell, even the idea of a battery reset feels strange, because I’m an old man who drives cars with all of the technical sophistication of a meat tenderizer. Also, the concept of resetting a battery still feels weird to me, unless that resetting is being handled with a chainsaw, the preferred method. But this button actually does seem to do something useful, something that should help address an irritating Achilles’ heel of hybrid vehicles. Let’s take a quick look at what this thing does.
In most hybrid or electric or even hydrogen fuel cell vehicles, there’s still a separate 12-volt battery of some sort to power all of those old-school vehicle accessories that aren’t worth re-engineering for higher voltages, like windshield wipers, lights, and audio system components, and so on. Sometimes the source of these 12 delicious volts is a conventional lead-acid car battery, and other times it’s a newer-style lithium-ion battery, either an independent unit or something integrated into the larger main traction battery of the car.
The 12V battery has been an issue on hybrids and EVs because, unlike conventional combustion cars that recharge the battery via their spinning alternators with every use of the car, 12V batteries on hybrids or EVs tend to be charged via a DC to DC converter, taking charge from the large traction battery to charge the 12V. The car has systems to detect when the 12V battery gets below a certain charge and then recharges it automatically.
Usually, at least. This doesn’t always work out, and if the 12V battery dies, your car becomes a big, immobile brick that can’t start until the battery can be recharged from an outside source or replaced. It can be a colossal ass-pain. That’s what this button is supposed to help with.
The way it works is if you get to your car and find it unable to start because of a drained 12V battery, this button should help you get out of that jam. Well, that is, after you manage to get into your car using the physical key hidden in the key fob and manually unlocking the door via the hidden key slot on the underside of the door handle, because normally all of that is handled with 12V electronics.
Once you manage to get into the car – it looks like the external power tailgate switch can open it if the key won’t or you don’t have a brick handy – pushing that 12V BATT RESET button will force the main battery to begin to recharge the 12V battery. You then have to start the car within 30 seconds. The recharging will then start from the main hybrid battery, and the combustion engine may not actually come on, at least at first. The owner’s manual says that when you do this, you should drive the car for at least 30 minutes to get the battery charged up, which almost certainly will use the gasoline engine on a hybrid.
The manual also notes that:
The following items may need to be reset after the battery has been discharged or the battery has been disconnected.
See chapter 4 and 5 for:
Power Windows
Utility View
Climate Control System
Clock
Sunroof
I get things like clocks, and maybe the radio and other presets needed to be reset, but power windows? Why do they care?
All of this is a little odd, for a number of reasons. First, I wonder why all of this isn’t more automated? Like, why does the owner have to push that button at all? If the 12V is below a certain point of charge, the car must be aware of that, right? So why wouldn’t it begin to replenish the 12V battery from the traction battery supply as soon as someone attempts to open/start the car? Is there a point to having a button to effectively jump the 12V system from the main power system? It just feels like if the car is capable of handling this from the push of a button, it could just as well make sure this doesn’t happen in general? Am I missing something crucial here?
Maybe there’s a good reason for the BATT RESET button. But it’s also strange because the 12V battery has become, in many of these systems, more of a concept than an actual object. If the 12V battery is just a sort of segregated part of the main battery, then the 12V battery has become more software than hardware, a mode in which a portion of the larger battery runs in, emulating the behavior of an old lead-acid battery. It’s a strange idea to consider. So when there’s a button just for resetting the battery, it’s taking the place of removing terminal connections or jump starting a battery from another car, or accidentally dropping a wrench on the two terminals until it glows red hot and melts.
The 12V battery is now, on many cars like these, the idea of a battery.
So, what does that button do? It doesn’t really reset the battery – whatever that may actually mean – but rather just recharges the depleted on-board battery from other on-board sources of power. It all seems a bit strange to me, though, like a strange half-solution to a problem that maybe shouldn’t even really exist anymore?
Top graphic image: Matt Hardigree
It’s worth noting that on some of the cars, like my Niro HEV (non-plug-in), that 12V battery is not a tradition lead acid or AGM battery, but a lithium battery that is both a challenge to source and (to a lesser extent) replace. That 12V reset button is a huge deal if that lithium battery goes dead, because jumping the battery or throwing a charger on it isn’t really a viable option.
I’m still stuck on how, and why is my door a jar.
It must be a problem that automakers have trouble with in general. My company’s E-Transit just had a recall to update the software that handles this very thing. Prior to the update it was prone to kill the (physical) 12V battery if the van sat unused for a few weeks. We never ran into that issue but the recall letter said it was a thing.
So whatever intractable problem prompted Hyundai/Kia to add this button also plagues Ford.
Still a better system than the Jeep 4XE, where a dead 12v battery will result in you being able to start the car, but do nothing else, including the ability to shut it off. You’ll then have to leave it running in your driveway until it runs out of gas, just to get it towed into the dealership for them to tell you that was all because of a dead 12v battery.
yikes