A power bank won't start a car simple fact.
OK, let me get in on this mud wrestling match. lol
What Nigel has been describing kind of already exists, and I actually have one.
Of course it can’t provide “instant” engine cranking like a traditional booster, but it simply recharges the “dead” vehicle starter battery in 5-15 minutes at 15 Volts @ up to 15 Amps.
I’ve tried to measure the actual current to see if it can really go up to 15 Amps, but I’ve only been able to measure around 4 Amps.
I think that’s because I was testing it on a fully charged good battery, and not a “dead” battery.
My favorite operating principal of this device is it provides two methods of connection.
Traditional alligator clamps for connecting directly to vehicle starter battery terminals, and a 12AWG CLA adapter.
This means you can “jump start” a dead battery from the comfort of the passenger compartment (while raining), and you don’t have to explain over the phone to your wife, and girlfriend how to connect Red & Black / Positive & Negative clamps, after you explain how to pop, and open the hood, and find the battery. lol
I purchased this device in 2018, and it was discontinued soon after.
It was only $20, I wish I bought more of them.
I took it apart recently, and it’s powered by (8) 18650 lithium-ion cells.
I’ve been meaning to make a YouTube video about it comparing it with a traditional booster, but my motivation was diminished because it’s been discontinued.
Let me go out to the garage and take some photos of it.