What could be worse than walking out to your car after a long day of work only to have a dead battery. Maybe you left an interior light on or your battery has simply reached the end of its life. Either way, car batteries don't typically give you signs of trouble until it's too late, and then your car just won't start. So no matter how old or new your car is, owning a working set of jumper cables - and knowing how to use them - is a must. First you need the right pair of cables. When you really need them, any set is better than none at all, but if you're buying new jumper cables, Popular Mechanics suggests ones that are 4 to 6 gauge and at least 20 feet 6 meters long.