It all starts with a car battery like this. 
Then they invented a backup battery that could give a quick assist, but it was almost as big and heavy as the battery! 
The Mazda sits so much without being driven that I’ve had a couple issues over the years with it not starting. I decided to buy a portable jumper battery to carry in it. The new generation jumper batteries look like this: 
The cellphone is there as a size-indicator. 
Technology marches on. (Either that or we’re getting all our improved technology from space aliens.)
Then they invented a backup battery that could give a quick assist, but it was almost as big and heavy as the battery! The Mazda sits so much without being driven that I’ve had a couple issues over the years with it not starting. I decided to buy a portable jumper battery to carry in it. The new generation jumper batteries look like this: The cellphone is there as a size-indicator. Technology marches on. (Either that or we’re getting all our improved technology from space aliens.)