My truck’s battery was discharged (forgot to unplug something), it was COLD, and I couldn’t find anyone to give me a jump, at least not quickly, and it was about a half mile away. I have 2-gauge jumper cables in the truck. Over a half dozen times these would start other cars being jumped that would barely turn over when the thinner “economy” cables didn’t. I literally just swapped cables and it would start right up. And these, which aren’t that much more expensive, can carry 600 cold-cranking amps over the distance. The typical thin ones make 13.5 volts at the running car about 6 volts at the dead battery, due to IIR losses; that’s not enough for the starter. I also have two big 8A8D AGM batteries for my solar, but I wasn’t about to try to drag them the distance. For my Harley, I happened to have a 540 CCA lithium battery, which I had at home. These are small and light weight, so I just carried it to the truck, used my 2-gauge jumper cables, and started my truck. I’m not sure about those smaller battery boxes that “can even start a bus”, but I just started my truck with my compact, lightweight lithium motorcycle battery. These batteries are also useful to put near your devices when your generator or inverter drops voltage or there is inductance (like a noise suppressor) in the long cables when something demands a surge (like a Ham radio transmitting 100w). – T.Z.