What sort of power bank is needed to jump start an EV?
February 2, 2025 3:34 AM   Subscribe

Can a power bank intended to jump start an ICE car also be used to jump start an electric vehicle, or does it need to be a specific type?
posted by Grinder to Travel & Transportation (15 answers total) 1 user marked this as a favorite
 
Yes, you can use it. See Jump Starting an Electric Car. Note that jump starting the 12V battery of an EV does not charge the high-voltage battery pack that is used for driving.
posted by amf at 3:54 AM on February 2 [2 favorites]


EVs have two separate batteries. One is a standard 12V battery that powers the controls, instruments, lights, wipers etcetera. There's nothing special about that one; if it's flat this would stop you from driving, but it can be boosted from any standard car battery, 'car-booster' powerbanks or another car. Note that it won't be recharging while you drive like in an IC car, so it'll likely go flat within a short time again.

The other battery is the one powering the engine, the voltage of which is around 400V. If you're thinking about putting some charge into a fully depleted one you need the mains ('granny') charger for your car and a device that has a storage capacity of at least a couple of kWh if you need to be driving more than a very small distance. One such option would be a (petrol-powered) generator, another would be one of the larger Ecoflow/Jackery/Bluetti or similar devices, with one or more auxiliary battery packs. With them you could power the mains charger which then recharges the engine battery. Slowly.
posted by Stoneshop at 4:55 AM on February 2 [1 favorite]


it won't be recharging while you drive like in an IC car

Not the case as far as I know. Some models even recharge the auxiliary battery while you're not driving.
posted by flabdablet at 5:26 AM on February 2


Ours at least doesn't AFAICT. The schematics show no downconverter from the traction battery circuit to the utility battery.

Basically, don't count on it unless it's documented to do so.
posted by Stoneshop at 5:49 AM on February 2


Also, a lot of the answers in that Reddit thread "they all do" based on the observation that their utility battery doesn't go flat seem to ignore the case that with nearly all EVs the utility battery gets recharged when plugged in to charge the traction battery.
posted by Stoneshop at 6:07 AM on February 2


Stoneship, a DC-DC stepdown converter that keeps the 12V low-voltage battery charged when the high-voltage battery is operating is common to every US highway-legal EV I'm aware of. Without it, there would be terrible scenarios during long-range drives during adverse weather conditions where the 12V battery would be drained over the course of a drive.

Do you perhaps have a very short-range EV not intended for highway use, like a golf cart? Your situation seems like an edge case.

Grinder, it is correct that the 12V battery in EVs can be jump-started like in an ICE car, but charging the high-voltage "traction" battery is far more difficult and would generally require a generator in order to do so if electric mains are not present nearby.
posted by eschatfische at 8:04 AM on February 2


Do you perhaps have a very short-range EV not intended for highway use

No.
posted by Stoneshop at 9:16 AM on February 2


Are there even any EVs that charge the 12V battery directly from AC power? I understood that the main battery was charged from the wall, then the 12V battery was charged from the main battery with the DC/DC converter.
posted by ssg at 9:49 AM on February 2


No.

OK, what EV do you own that doesn't have a DC-DC converter to charge the 12V when the traction battery is in operation? All of the earliest models of the modern (2010+) generation of US and EU EVs (Leaf, i-MiEV, Tesla, derivatives like the RAV4 EV) have DC-DC converters as far as I know. If you have something especially exotic or vintage that's fine, but that doesn't help with OP's question. Genuinely stumped here.
posted by eschatfische at 11:30 AM on February 2 [1 favorite]


We should be really clear about what we are talking about when we say jump start an EV. As mentioned before, there are two battery systems in modern EVs, three big one you drive off of and a 12v just like other cars. The 12v runs a bunch of the systems needed to start the car, charge the big battery, open the doors, etc. That 12v is usually recharged by the bigger battery while the big one isn't charging. This can be while driving or when "off". Eventually, these 12v batteries wear out. A jump can get it working again and able to start the car. A battery pack style one should do fine, as would a trickle charger. What these can't do is start a car that ran out of power in the big battery. That's a different story.
posted by advicepig at 7:00 PM on February 2 [1 favorite]


True. The pure-electric equivalent of a portable gas can is one of those multi-thousand-dollar generator-replacement battery packs, which hold maybe 5kWh of energy.

Even if you could arrange for the voltage up-conversion that would let a typical jump starter push current into an EV's charge port, their energy capacity is only around 0.2kWh so it wouldn't be worth the bother. The ICE equivalent of that manoeuvre would be trying to drive away on the starter motor.
posted by flabdablet at 8:32 PM on February 2


The saga here, and in the Part 2, has a lot of info about what gets difficult when an older hybrid's batteries are fully discharged. As noted above, the 12 volt battery is pretty much the same as in any other car.

A dealer will have equipment that can charge the big battery. Usually, it would only need a bit of charge, enough for the on-board computers to think it is in working order. That would get the engine going.and the big battery will be recharged in the normal way.
posted by SemiSalt at 5:21 AM on February 3


SemiSalt, the video you linked to is about a conventional ICE (gas-powered) car with a depleted 12V starter/accessory battery, not a hybrid or BEV. Saab did not commercially produce any cars with any sort of electric drivetrain.
posted by eschatfische at 2:45 PM on February 3


I should have been more careful. I think I meant this one about a Toyota hybrid.
posted by SemiSalt at 6:52 PM on February 3


Or there's this one about a Fisker Ocean.
posted by flabdablet at 9:37 PM on February 3


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