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Electric Car FAQs: Can You Jump-Start an EV?

Electric cars are just like gas cars — until they’re not. In this FAQ series, we’ll explore that 1% of the time that EVs are just different enough to require some explanations.

Supporters of EVs will tell you that electric cars are just like regular cars. For the most part, they’re right. You step on the pedal on the right and the car goes, you turn the wheel and the car turns, and the only real difference is what kind of fuel goes in it. We say stuff like that all the time, in fact — if we’re being completely honest, though, that’s only mostly true. 99% of the time the only difference is what kind of fuel goes into the car, but that last one percent probably needs explaining.

To provide that explanation, we’re launching a segment of “Electric Car FAQs” to answer those oddball questions that come up one percent of the time. Today’s question: Can you jump-start an EV?

Electric Car FAQs: Can You Jump-Start an EV?

Image credit: Kyle Field | CleanTechnica

It’s a common experience — you walk out to your car one cold, winter morning, and it won’t start. Maybe it chugs along for a second or two before you hear that dreaded “tick-tick-tickickick” and then, nothing. Your battery is dead, and you’re going to need a jump to get going.

If you have an internal combustion engine (ICE) powered car, you don’t need to wait around for Roadside Assistance or some futuristic tow truck to show up. All you need is another one and a set of jumper cables. Then it’s red-red, black-black, turn the key, and that’s it — you can get where you need to go (which, at this point, is probably somewhere that sells car batteries). Again, we’re not covering any new ground here, but what happens when the car with the dead battery is electric? Can you jump-start it?

The answer is a resounding and assertive, “it’s complicated.”

See, conventional ICE-powered cars have a single 12V electrical system. That means their 12V car battery powers the lights, the power windows, the heated seats, the onboard computers, and — its heaviest load — the electric starter that cranks the engine.

Hybrid and electric cars work a little differently, however, in that they have two electrical systems. The first is a 12V system that would be familiar to most shade-tree mechanics because its battery does all the same stuff the 12V battery in a gas car does. It powers the lights, the seats, and the onboard computers … the very same onboard computers that both turn the car “on” and manage the charging for the 400 or 800V batteries that you probably think of when you hear the words, “electric car battery.”

That’s the long way of saying that, if your 12V battery dies, it’s not going to power up the ECU and CAN bus, and it’s pretty likely that you’ll be stuck, unable to convince your car to move under its own power. That’s the bad news. The good news is that, yes — you can quickly and easily “jump-start” the 12V battery and, assuming you have some electrons in the “tank,” get on your way. What’s more, it’s done in just about the same way as the ICE car you’re probably used to.

How to Jump-Start an EV

  • The first thing you need to do is make sure your EV is disconnected from the charger. To repeat, DO NOT attempt to jump-start the 12V battery while the car is plugged into an outlet or — worse! — a DC fast charger. Doing so could do cause serious damage to people and property. Unplug the car.

  • Assuming you’re using another car (not a “jump box”) to jump-start your EV, position the two cars close enough to each other that the cables can reach both 12V batteries, but not touching.

  • Make sure both vehicles are off, in “park” (or, in a manual-transmission car, neutral), and have the parking brake engaged. If you are using a jump box, just go on to the next step.

  • Turn everything off. That means the headlights, windshield wipers, interior dome lights — anything that will draw on the battery.

  • Connect one of the RED positive (+) clamps to the positive (+) terminal on the “dead” car battery. Being careful not to let the black and red connectors touch, attach the other RED positive (+) clamp to the positive (+) terminal on the “good” battery.

  • Next, place the BLACK negative (–) clamp to the negative (-) terminal on the “good” battery, then connect the BLACK negative (-) clamp to the negative (-) terminal (or a grounding point) on the “dead” battery.

  • Make sure that the cables are clear from any moving parts (we’re talking about an EV here, so there shouldn’t be many), and that the clamps securely attached to the battery terminals on both cars.

  • Start the “good” car, and leave it running, or “on.” Note: if the “good” car is ICE-powered, do not sit there revving the engine — just leave it idling, as the alternator should be providing more than enough current to jump the “dead” battery.

  • Finally, try to start the EV with the “dead” battery. Once it’s running, you can disconnect the jumper cables (as before, be careful to ensure that the clamps don’t touch each other until both batteries are disconnected).

It’s worth noting that this process will also work on a PHEV or mild hybrid as well — it’s the same series of steps, except you’ll hear a “Vroom” when the ICE engine starts. In a pure BEV, if there was any juice left in the “main” EV battery, you should be able to get to your dealer/local auto parts store and get a new 12V battery without issue.

I Did All That, It’s Still Dead

Let’s face it, there’s no good time for the 12V battery to get fully discharged or run down to zero. In an ideal scenario, you’ll have some residual charge in your vehicle’s larger battery pack and still have some range — but what if the 12V dies at the worst possible time, and you really don’t have any range to speak of? Or, like, at all?

Image courtesy Lightning Mobile.

Mobile charging stations capable of bringing a DC fast charger to you do exist, and they’re becoming more common in dealer service and towing fleets as the electric car market grows. Last year, we covered one solution from Lightning Systems that’s equipped with 192 kWh of high-energy-density, liquid-cooled DC batteries designed to be installed in a vehicle or trailer for rapid mobile deployment. That system, marketed to fleet services, helps keep vehicle uptime high, but could see more widespread adoption as commercial fleets (think “taxis” and “rental cars“) become more and more electrified.

For large events like tailgate parties or e-mobility festivals, Tesla has developed a trailer-based DC fast charging bank that will bring its excellent Supercharger Network wherever a crowd of EVs might show up — and that technology is just going to get smaller (and cheaper!) as time goes on. You can check that out for yourself below.

Once you’ve got some charge in the big battery, you should be ready to go wherever your needs take you. Just remember, a 12V battery that goes dead may not be able to hold a charge, even after it’s been jumped. You’ll definitely want to head to your dealer or local auto shop to get it tested and/or replaced as soon as possible.

We hope that’s answered your Electric Car FAQs for today. You’ll be able to read more FAQs as we expand the series (this is the first one of these), and if there’s an electric car question we haven’t answered for you that you’re dying to know the answer to, scroll on down to the comments section and share it with us. Until then, drive safe, and drive clean!

Original content from CleanTechnica.

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Written By

I've been involved in motorsports and tuning since 1997, and have been a part of the Important Media Network since 2008. You can find me here, working on my Volvo fansite, riding a motorcycle around Chicago, or chasing my kids around Oak Park.


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