EV cars are thick!

Of course it can. How many times can you try to turn your car's engine over with a 40-60Ah lead acid? A 3Ah can clearly do it once or a few times. I'm not making it up, they sell them as boosters, go look online. They also have a USB port to charge phones.

So the wrong type of electricity was left in the car? You'd think a Japanese car would be designed better. Although considering my Honda's idea of 4WD, maybe not.

Never the case. Even if you need to weld big lumps of steel onto the chassis, it's cheaper than buying another car.

Indeed. I assumed you'd bought an old second hand one when you mentioned the problem.

You could fit a bigger battery, or more of them. Or fit a switch to disconnect it when you park it. My 21 year old Renault petrol car's battery goes flat in a few hours, I think it's the alarm system, although the alarm never sounds. I simply undo one of the battery leads every time I park it. Harder for a theif to steal too, he'll think the battery's flat.

Jump start batteries tend to be rated at 10Ah or more and claim to be able to output 100A+ (for a very short period) The construction of the battery is many individual plates wired in parallel in order to provide a large current.

That one, is three flat cells laid on top of one another, to make a "12V or so battery".

The battery operates out of spec, when it jump starts the car. This will shorten the lifespan of the flat cells. And Big Clive demonstrates there, the time constant of tolerance (how long it takes to swell the thing up when driving into a short circuit).

The "current rating" on those things, is mostly imaginary, because things like the cables to the battery, are too thin for the stated amount of current. Just the fuseable link in the diode blob, opens at too low a current to test that "rating scheme" they use.

One jumpstart pack, gave itself a rating of

Paul

But then the mass and the dimensions of the battery are different. A leisure battery is a lot heavier than an automotive cold cranking amps battery. It's one of the few cases, where you can "feel you got your moneys worth".

Paul

While the specified instantaneous current output of these packs may be greatly exaggerated they do work to start a car.

I have one rated at around 12Ah capacity and have used it twice to start ICE cars where the car's battery has gone flat enough for the starter to barely turn the engine and after a few attempts not to turn the engine at all.

The 20000 number is probably the miliamp hour capacity, not the number of ampa it can put out. However some are advertising numbers of 2000 to

Hard telling where are pulling the numbers from, like some computer speakers advertise 100 watts music power and are powered by a one amp wall cube.

How do you use them? Do you connect the jumpstart battery to the dead battery and try to start the car immediately, trying to draw a couple of hundred amps from the jumpstart battery? Or do you have to leave the jumpstart battery in place for some time to allow it to transfer some of its 12 Ah into the dead battery at a comparatively low rate (ie low current), and then try after the dead battery has taken on enough energy to spin the starter motor? I presume you don't get many chances to start the engine, and you're out of luck on a freezing cold day when the engine oil is cold and viscous.

Do any car engines make use of "valve-lifter" technology (as used on some motorbikes) to open the exhaust valve during starting to prevent any compression while the engine is running up to a speed at which the momentum in the flywheel (plus less power from the starter motor) will be enough to fire the engine once the valves close and the engine runs normally?

When I've used my power bank it was connected to the car's battery for around 15 seconds before starting the car

Possibly two attempts. When I had to charge the power bank after one car start the 4 charging LEDs indicated it still had 50 % charge.

For my car start power bank, the wires to connect the power bank to the car battery are VERY short. They are just long enough to reach across the car battery terminals with the power bank sitting on top of the battery. They are not the traditional long jump start leads used to connect one car battery to another car battery.

It does in fact work fine with those.

Yes, and that works fine.

Nope.

Nope, I have in fact done that fine with a substantial diesel engine of my neighbours.

None that I can think of.

I don't, particularly with the car owner starting the car when I tell them too, just after I connect the jump starter.

It takes a little longer when I am doing it by myself because I have to walk from the front of my car to the drivers seat so I can start the car, but nothing like 15 seconds.

I did have to try a few times with one of my mates big diesel suv but it showed no sign of turning the engine over more slowly at the end and the digital display of charge remaining didnt drop much at all.

They are all like that, very short very thick leads.

Lithium cells used to power model planes can be flattened in about 2 minutes reasonably safely, so a 10Ah battery could easily deliver 300A. I dont know what capacity they sell for starting cars, but high discharge rates come with modern lithium cells.

The discharge rate in LiPo batteries are indicated by the C number. Many of them are 50C and 100C. 50C means it can discharge at 50 times the rated capacity, while 100C means it can discharge at 100 times the rated capacity.

For example, this LiPo battery advertised on Amazon is 8000mAh (8Ah) with 100C. That means it can discharge at 8A x 100 = 800A.

One of my smarter purchases was a (then "lead" based) portable jump pack way back 1980 or so. Hate to tell you how many times I used it. Not so much for me (well, I did buy it after I left my lights on..) as in helping other motorists.

Oh... *and* ... in the 2003 NorthEast US blackout, I hooked it up to a local store's telephone system, which kept them connected for the next ten hours...

I've since upgraded to much smaller, lighter, and similar powered Lithium units, which are "smarter" than my original

These generally (I've used/gifted about a half dozen), will have "full" output - usable for starting cars - for 15 or so seconds, and then shut down. You can then reset them and try again [a].

They *also* have a lower continuous output via USB ports which can run for hours...

So you probably CAN'T, unless you wire something up through the USB connections, use them to charge your car battery. And that would be a slow charge for only a few percent.

Turned out I'd get a dozen feet or so, and then they'd shut down.

So it was a nice idea, but didn't work...