Jump starting a car with a Cell Phone

One of the guys here at work claims to have jump started his 87’ Saab with a cell phone. One night his battery had run down so that the engine would crank(the ruh-ruh sound), but not start. He then plugged in his phone to the cigarette lighter via the charger and then could start his
He thinks that the extra battery power from his cell phone gave him the extra oomph to start the car. I think he is wrong, my explaination is that plugging in the phone caused the resistance in the electrical system to drop enough for the battery to start the car. I once read in an old popular mechnaics that if the car will crank, but not start, you should turn on the headlights and then try again. This worked for me on more than one occassion. We had the opinion of an electrical engineer, but he went into
calculus so we stopped listening. The question is why did the car start?

He got lucky.

Sorry for being abrupt; I had to take a kid to school.

I don’t know about your friend’s phone, but my wife’s Sprint phone uses a 5.5 volt adapter to charge the battery. The voltage regulator in the adaptor can drop the 12 volts of the car down to the 5 volts of the phone, but it can’t boost the 5 volts back to 12.

Even if it could, It wouldn’t matter, as the phone’s batteries would supply a lot less than an amp of current to the starter, which is probably drawing over 50 amps from the battery. To sum it up, he got lucky.

FWIW - you can buy an emergency jump starter that plugs into your car’s lighter, so it’s definitely possible to start a dead car by powering it through this channel.

Click & Clack recently addressed these type of products on their show. Their conclusion was that such a device would work if your battery was barely dead, and then only in certain conditions (warm enough temperature for one).

Perhaps trying to start the car the first time warmed the battery up. Warmer battery = faster chemical reaction = more power = engine starting.

I cold probably prove this using calculus, but I don’t want to put anyone to sleep. :slight_smile:

Probably a good assessment, and it sounds like good fodder for Tom & Ray. For starters, no pun intended, if you DID draw a significant amount of the amperage required to run the starter motor through the cigarette lighter cicuit, you would blow a fuse.

If you discharge a battery to the point that it will not turn the starter and then wait for 15 minutes or more - preferably more - it will often turn the starter over when you try it again.
I was told this was because ions formed during the discharge cycle, in effect shield the plates and prevent flow. The ions will be absorbed into the plate over time and a few more amp-hours/minutes become available.

A starter requires from 75 amps to more than 150 amps to turn the engine, so a cell phone battery or other small battery absolutely will not operate it. They will not provide the required amperage.

Or it could have been one of those Chyrsler/Plymouths which often needed a new starter relay but they would often start if you tried enough times. Eventually the relay would catch on the second or third try.

First, if the car is cranking (ruh,ruh,ruh,…), the battery is doing pretty much all it’s suppose to do. Starter motors, like Diver said, draw 100 to 200 or more amps. If the battery has enough juice to do that, it surely has a couple of amps left over for the ignition system.

Second, I was given one of those lighter to lighter battery chargers for a present. They tell you not to try to start the car with it connected. It is to charge the battery, not to start the car. Lighters are fused for about 20 amps. That little 16 or 18 gauge wire can’t handle that much current, much less the 100 amps that might be drawn across it when you hit the starter. Definately not something you want to do with the cord laying across your lap.

Third, if your engine is cranking, you don’t need a jump in the first place. If the engine is turning over, a lot of other factors come into play as to why it doesn’t start, but a minor change in voltage would be about the last thing to worry about. If the voltage drops much below 12 volts, the starter is going to stall. So, if the starter is working, you have plenty of voltage to run the ignition system.

Fourth, with many things, like cell phones, when you connect them to an external source, the cable connection cuts out the battery so that you are powered directly from the external source. Even if that weren’t the case, I would doubt that the battery in a cell phone could power the dashboard lights more than a few seconds before running down, much less any major part of a car’s electrical system.

I can see that if you were having trouble getting the car to crank, that maybe by putting a smaller load on the battery, like turning on the headlights for a while, could warm up the system and it would be more likely to be able to crank the engine.

Other than that, the only explanation I can think of is that he used his cell phone to call AAA, they put some gas in it, and sure enough the car started.


Those electric batteries that plug into the lighter have been exposed many times as being pretty much worthless. Consumer Reports for one said that much. They just add a little charge to your battery. And yet, I have seen them several times in news programs touted as the latest gizmo. Those newspeople just don’t have a clue and do not do their homework.

Any device that has an adapter that plugs into the car lighter cannot supply any electricity back to the car as the adapter only goes one way.

cornflakes is right on the money. There is no way the cell phone had anything to do with the car starting.

It reminds me of what my friend calls “the fruit dance”. My friend studied monkeys at one point in his life. They dropped fruit in to the enclosure at random times. The monkeys would try to figure out exactly what they were doing just before the fruit appeared (maybe scratching themselves in a particular way, or jumping on one foot or whatever), and would later do that same thing again in the attempt to get more fruit. My friend called this the fruit dance.

PATC, your friend is fruit dancing with his cell phone.

I came across this thread when I was stoned and reading an article about new ion batteries. Then I wondered if it was powerful enough to jump start a car and if there were any apps/external cell phone adapters and Googled “app to jump start car with cell phone”. This thread was at the top of the search results.

This is a link to portable smartphone battery that can jump your car.


This was from 2014 and it was just a portable cell phone battery that was powerful enough to start your car, and charge your phone. Three years has passed. And with the creator of the ion battery claiming new cell battery is three times more powerful than current ion batteries, soon you will be able to jump with your cell phone and not lose battery life.

Cool – this thread was indeed a zombie worth reviving. Fun to see the technology evolve.

(And, incidentally, this revival has made it possible to add “fruit dance” to my vocabulary.)

I have seen an infomercial playing on TV for that exact product, so it certainly is available now.

There’s a ton of 'em on Amazon.

These aren’t really cell phone batteries, they’re several times larger. They’re small battery packs that can jump start a car and also have a USB port that can charge a phone.

I’ve had one of those small battery packs for several years. I’ve used it a few times to jump start a car with a dead battery. It mostly works, although one time it failed because it said it needed to be recharged; but when I plugged it in to recharge it, it said it was fully charged after about 5 minutes. I still don’t understand what happened there. It couldn’t really have been discharged if it recharged in 5 minutes.

that would have to be only useful if the battery was just barely discharged, and you’ll have to wait a while. your car’s battery is rated roughly at 50-80 A-h, a 6,000 mAh (6 A-h) isn’t going to be able to rescue it if it’s significantly discharged.

Plus the notion that that piece of junk can deliver “300 amps” of current is highly suspect, especially through those dinky cables.

If the infomercials are to be believed, they used one of those to jump several cars in succession that had their batteries removed. I can’t vouch for that, of course, since I don’t have one and haven’t used it first-hand.