Mechanics here in Boston call this a “jump kit.” It’s a briefcase-sized, 20lb, 12V battery with built-in 12v/120v charger, and with built-in jumper cables attached. The Jump-N-Carry is a much easier way to jump a car; no jockeying the live car to kiss bumpers, no stretching jumper cables between cars. I tend to keep mine in my car, so it’s quick & easy to help anyone who needs a jump. A cute trick for a dead alternator is to hook up the jump kit, lay it inside the engine well, close the hood as well as you can, and drive to the shop. One of my mechanics has a J&C with a case that melted from doing this trick, but it still works fine.
This model can be charged from your car’s cigarette lighter, but I just plug mine into a wall outlet with any extension cord that’s handy. It holds its charge for months without recharging. I’ve had one, trouble-free, for a year and a half.