What happens when your EV Hits Zero Percent State of Charge?

With misinformation - or inaccurate information - rife on electric cars, whether it’s on social media, or even in the mainstream media, we aim to dispel some myths and provide some facts here at CtrAltRefuel.

And recently the topic of what happens to EVs when they reach a zero percent state of charge caused a stir, so we want to explain exactly what happens to ensure that drivers are in charge of facts, and not assumptions.

The comparison was made between petrol cars and electric cars with the comments that when the petrol car gauge points to empty, there maybe another 40 miles in the tank. And maybe is perhaps the key word here, because it’s a bit of a guess, but invariably there may be some fuel remaining at the bottom of the tank that the gauge hasn’t picked up.

When it came to EVs, the debate centred around an assumption that when an EV hits a zero percent state of charge (the equivalent to an empty tank) that the car stops and may shut down entirely.

So What Does Happen at 0%

EVs have a buffer  – and a far more accurate one than found in an internal combustion car. EVs do not on the whole cut out the second the display hits 0%. Manufacturers deliberately leave a protected reserve ‘buffer’ below the displayed zero marker (and also above the displayed 100%, too).

This prevents deep discharge damage to the battery cells and gives drivers a safety margin. In a similar way, petrol or diesel cars should not be driven until they’re out of fuel, too, because damage to the fuel pumps may occur.

However, there are controlled, real-world tests prove EVs have a below zero buffer.

• CarMax drove an EV to the displayed 0% and kept going for another 15 miles.

• Independent tester Bjørn Nyland has many “zero mile” tests across Teslas, BMWs, Audis, Nio, MG, and many more. The cars keep moving past the on-screen zero, usually in reduced-power “tortoise” mode.

• Kia owners have reported ~20 miles of reserve in limited-power mode below 0%.

• Broader data shows many drivers continue for several kilometres (sometimes 10–20+ km) drawing on that hidden buffer.

In each situation there were numerous warnings, on the drivers display and central screen in some cars. When reaching a critically low state of charge, the car’s power is throttled back reducing top speed and acceleration in order to preserve power so the driver can safely pull over.

This is often referred to as ’Tortoise Mode’, or ‘Turtle Mode’ and the throttling starts just before reaching zero miles of indicated range.

And it’s similar for petrol cars, too. Because if you find yourself critically low on fuel in the tank, the car’s power may be reduced (in modern cars) to ensure safe passage to the side of the road, so it just doesn’t cut out in the middle lane, for example.

What About the 12v Battery?

So, if your EV has consumed all power from the high voltage battery, what happens when its stationary and cannot be moved?

EVs also have a 12V battery, just like an ICe car, and this 12V battery powers the ancillary systems like lights, hazards, screens etc, so even once your High Voltage battery is depleted - and the car won’t move any more - all these systems will stay alive until the 12V is also depleted.

Can EVs be Pushed When The Battery Has Been Depleted?

You may hear comments like “You can’t even push them!” when the high voltage battery has died.
Well, quite simply, you absolutely can. Just like any automatic fossil car, you need to be in Neutral, or be able to select Neutral, so long as your 12V still has power, (in an ICe or EV) then you can simply select this.

However, for some EVs, the car may need to have the ‘no regen’ option selected, as on many EV’s the variable regen is accessed via flappy paddles behind the steering wheel, or a mode setting in the cars user interface, or even a button. For those of you with an EV that have used one of them roll-thru conveyor car washes, you’ll be aware of this and also need to select this mode.

The caveat to this is that cars are generally heavy machines and pushing any modern car is hard work. EVs are no different as any car weighing in at 1500 kg - 2200 kg is a heavy mass to push irrespective of its powertrain.

But, to push most EVs short distances, there’s a couple of points to consider:

•  Shift into Neutral (powered by the 12V battery)

•  Many EVs have a specific “Transport Mode” or “Service Mode” for flatbed loading. And interestingly, even when you have not been able to get the car to move any further under its own power, there is often a service tow mode that allows the recovery person to get the car to move on to the tow truck.

Towing, like with any automatic ICE car, is not something that is recommended and requires a flatbed or dollies (wheels off the ground) to avoid spinning the motors and generating unwanted voltage – this is not an EV-exclusive issue. In fact, any automatic ICE car must not be towed, but you can certainly push them short distances provided they have been shifted into Neutral.

Key Points to Remember When Broken Down

If you do breakdown in your automatic ICe car or EV, when safe to do so, ensure the parking brake is on and put it in neutral (and select the no regen mode soon as possible). But don’t be too concerned if you can’t do that if - for example - your 12V battery dies, as just a little bit of power from a 12V booster will be all that is needed from the recovery person.

Note: I always carry a small 12V jumper with me. To date, I’ve only ever used it to jump start incapacitated fossil cars. Something I come  across a lot in my job.

Do Petrol and Diesel Cars have a Big Reserve?

In short, yes they do because when that dreaded yellow low-fuel light comes on, there’s fuel left in the bottom of the tank that goes a fair way until the car conks out, provided the gauge is accurate of course!

The comments on social media referred to a “hidden 30 mile buffer”, but this isn’t accurate, either. I’ve run out of fuel a few times over the years, despite the gauge indicating it wasn’t totally empty, so take those analogue gauges with a large pinch of salt.

More importantly, running the tank dry can damage the fuel pump (which uses petrol/diesel for cooling and lubrication) and can suck up sediment from the bottom of the tank. That’s why the “buffer” exists – as a last-resort safety net, not as a usable feature on a regular basis.

Running either an EV or ICE car to true empty is a bad idea. ICE just hides the risk behind a vague analogue gauge, whereas EVs actually give drivers more precise information, such as:

•  Exact percentage remaining (not an analogue needle or system)

•  Real-time energy consumption

•  Navigation that plans charging stops and accounts for weather, speed, elevation, and preconditioning

•  There’s over 120,000 chargers and you’re never likely to be far from one no matter what time of the day, plus chargers are open 24 hours of course, unlike most petrol stations.

In practice, most EV owners treat 10-20% as their personal “time to refuel” prompt and rarely go lower. Same for a lot of people with their petrol gauge, but as previously mentioned, there are many warnings before running out of charge. It’s hard to ignore.

Conclusion

The claim that EVs “just stop and die at zero” while ICE cars have a generous safety net is a distortion. Both technologies usually have reserves. Edge cases can exist for both too, and both can leave you stranded if you ignore the many warnings. EVs make the remaining energy visible and manageable, and they include engineering buffers for a reason.

Pushing any car is difficult, and towing requires a proper flatbed, just like all automatics.

Personally, I have never run out of electricity, or ever seen the dreaded turtle on the dashboard, but I have run out of petrol. However, when the recovery services arrived, they weren’t carrying any spare fuel, so the car was recovered to a petrol station instead.

Similarly, if you run out of charge, you may be recovered to the nearest charger, but there are some recovery services that will now send out a mobile charger to get you moving again so you can at least reach a rapid charger.

If you are genuinely curious about real-world EV behaviour at low charge, watch Bjørn Nyland’s or Out of spec Studios zero-mile tests on YouTube, or talk to owners who’ve actually driven one to the edge. The data is out there.

Drive safe – whether you’re sipping electrons or hydrocarbons, but it’s never worth playing ‘Petrol Bingo’ or gambling on that last few percent in your EV, either!

Author

Newt is a lifelong car enthusiast and specialist in electric cars.

You can find Newt on𝕏 at @eV_Newt