Can you pushstart a hybrid / fully electric car?

Question

I'm fairly new to mechanics and was wondering:

Let's say you have a hybrid car and the battery is dead. Can you pushstart this vehicle?

The same question goes for a fully electric car, however I'm not sure if there are any manual-electric cars. If there are no manual fully electric vehicles, let's just pretend like there are, would this still be possible?

I personally think this won't be possible since they're all electro motors compared to the petrol vehicles which uses compression of fuel to 'run' the motor. Please correct me if I'm wrong!

Answer 1

There are two reasons why a modern hybrid car could fail to start due to lack of electricity. Two reasons, because every hybrid car has two batteries (12V and HV).

One is that the 12V battery is flat. You cannot push-start it then, as the 12V battery boots up the computers that connect the relay of the high-voltage (HV) battery. No computer boot up, resulting in non-working motor-generators. No regenerative braking then.

The second is that the HV battery is flat, but the 12V battery may or may not have power. The HV battery is at least in Toyota and Lexus hybrids used to drive the motor-generators (MGs) MG1 and MG2. These together start the engine using the power from the HV battery pack. So, there is no conventional 12V starter motor in these hybrids.

If you have a flat HV battery and 12V battery that is not flat, in theory you could power up the computers of the hybrid car. However, I don't believe any hybrid car manufacturer has added the code paths to charge the HV battery with regenerative braking when the HV battery is flat. It would most likely be a software-only change, but I don't believe the required code lines are there... Most likely it tells you to contact the dealer and refuses to work.

So, the answer is most likely no. If the 12V battery is flat, you need to jump-start it or charge the 12V battery. Push starting definitely won't work as the computers cannot be booted up. If the HV battery is flat, I don't believe regenerative braking would save you, but I might be wrong.

By the way, in Toyota/Lexus non-plug-in hybrids, if the HV battery is flat, only dealers can recharge it using a special charger. Minor garages won't have access to the charger. However, this is a very rare issue, as every line of code in the computers of the car has been written to save the HV battery from charge depletion. If it looks like the HV battery would become empty, the engine is started to charge it. The only remaining issue that can't be solved is self discharge, but that would take months of non-use to cause any problems.

Now, which one is the most common issue? It is definitely a flat 12V battery. Leave the lights on, your 12V battery is flat. Don't replace your 12V battery for 10 years, it will most likely be flat (whereas the HV battery is designed to last the lifetime of the car, i.e. 20 years). Don't drive the car for months, the small constant drain on the 12V battery also makes it flat (whereas the HV battery is disconnected by using a relay).

Answer 2

I just rebuilt the front end on My 2004 Honda Civic Hybrid with a 5 speed manual. It was in a minor accident and sat for several years. Both batteries have somewhat degraded. I would jump start it every so often.

So i pulled it out the other night and my alley mechanic friend did the alignment with a piece of twine. It started on its own, but after sitting for several hours with the key turned and door open, both batteries died. The dash just barely lit up.

There was no other car around so we decided to try and push start it. The gas motor did start, but it was not running right and the dash was partially dead. It would not run above idle and after a few minutes it stalled. My neighbor brought a jump pack, and it fired right up with the quiet hybrid battery starter(not the noisy 12v backup starter) and ran fine.

With the honda hybrids, i think the car relies on the 12v to set the relay for the hybrid battery pack to start the car.

Answer 3

No, but you can jumpstart or recharge by towing

In hybrid and full electric cars (at least the Toyota Prius and the Nissan Leaf) they usually have a 12V battery and a traction (or high voltage) battery. The 12V battery is used to “boot” the car like BIOS of a PC and to power accessories. If this battery is dead the only way to start the car is by jumpstart by using jump cables. Since the 12V battery usually is very weak one, since it is not used to run the engine starter in hybrid cars (the electric engine does by drawing power from the traction battery instead), it cannot be used to jumpstart an internal combustion engine (ICE) car but the other way or between either hybrid or electric cars should work.

After the car has “booted”, if it is the traction battery that is dead and either you have no gas or it is a electric car you can recharge it by towing the car or rolling it downhill. I once had a problem with the gas engine of my Prius and I just kept rolling the road downhill until I found a safe spot to park. The only nuisance was that here was a huge red triangle in the dash and when I drove through a small hill the battery almost discharged completely. Mind that manufacturers usually don’t recommend doing it this way and in a hybrid car this does little help since the traction battery is only good for about 1.5 mile.

EDIT: Since you mentioned about manual electric cars. Almost all today’s electric cars have only one speed and the electric engine can stop without stalling, thus no clutch is needed, and the wheels are attached directly to the engine. Hybrids use can use any gearbox like gas cars, but the most common is CVT with planetary gears. The first generation Honda Insight and the Honda CRZ have manual gearbox optional, thus it might be possible to push start these. There some hobbyists that converted manual ICE cars to electric and kept the old gearbox, but the clutch and shifting is rarely needed as result. Some older electric cars have some odd architectures, like the fist generation Tesla Roadster which has an automatic two speed gearbox. I guess that here may be a few older electric cars with manual gearbox

EDIT2: Just read in a forum that it is possible to push start a 2000 or 2001 Honda Insight, but the results tend to be dire (car just barely drives, a very few times it works well). Honda patched the ECU in the 2002 model so that this is not possible anymore and I guess that this has been carried over to the Honda CRZ. Jump starting is the only only way to go here.

Answer 4

I'm by no means an expert on Hybrid tech, but I would say it is largely dependent on 3 factors:

1. The design of the car's electrical system.
2. How dead the hybrid battery is.
3. Why the battery died, and for how long it's been dead.

Most of the hybrids I've been in/driven do have some kind of regen system that would allow you to feed energy back into the battery bank... however, that does require getting the 3 ton (US) thing moving. That's the hard part! Then, once it is moving, you have to keep moving it against the resistance of the regen system. This is where design comes into it. If the system was extremely efficient, you may be able to get enough juice from a good hill to move a bit further, but basic physics would dictate that you wouldn't be traveling far without more added energy.

The other point about how dead the battery is would come into play as well because if it was fully depleted then probably wouldn't be able to engage any of the regen systems to begin with... so you'd basically just be towing or pushing the car.

Finally, why the battery died and for how long. If it just died from driving, then you may be able to get it a little more juice. But if the battery died due to some actual system fault (like cell failure), then you probably won't be able to regen it anyway.

In any of these cases, with a hybrid, you gas motor should be able to supplement needed energy. As Paulster2 mentioned, they usually have split power systems, however since there's no permanent connection between the gas motor and the axles, it would be very unlikely that (even with a manual transmission) you would be able to put the torque all directly to the gas motor and force it to start.

Now this would be dramatically different with a 100% EV. They rely entirely on regen, so in theory you could push one with another vehicle and build some energy, but that would require another vehicle which would kind of null the whole problem.

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Anyway, like I said at the beginning, I'm not an expert, this is just based on my opinion. If you'd like I do have some friends that specialize in hybrid repair (although specifically US Priuses is what they do). They may have some better insights if you'd still like.

Answer 5

Posting a second answer because the answer to push-starting electric cars is entirely different from push-starting hybrid cars.

With electric cars, the law of conservation of energy applies. If you manage to push the car to a speed of 10 km/h, and then manage to charge the batteries using regenerative braking, then you have in your batteries juice to at most accelerate the car to 10 km/h. Accelerating to 20 km/h would be a violation of the conservation of energy.

And note that the 10 km/h acceleration is possible only once. Then you have run out of juice, and you cannot maintain that speed.

If you consider acceleration to 10 km/h and then being unable to maintain that speed acceptable, then perhaps you could push start an electric car. But most people won't consider that as a successful push start.

And also, with electric cars the code paths reason in the software code applies. The code paths to do regenerative braking when the battery is empty may not be there.

Furthermore, all of this assumed the computers can be booted up. If also the 12V battery is flat, your computers won't be booted up at all.

So, in fully electric cars you would be better off by using human power, i.e. have somebody continuously pushing the car forwards. Converting that human power to electricity and back to mechanical energy is just insane.