Cars run on two components; fuel and electricity. While we commonly think of an automobile as being a a "combustion engine, " there is a lot of electronics and electrical components that are critical. The primary power supply for these components is the battery. Batteries can fail for numerous reasons, including; the wrong battery for a particular type of car, corroded battery terminals, worn battery cables, and "dry cell." Defective batteries can cause severe burns and in some cases, fires and/or explosions.
The starter is an electric motor that consists of several brushes, which carry pulses of electrical current that gets the motor to spin and therefore "turns over" the engine. Sometimes one or more of these brushes "burn" and no longer enable any electrical current to pass through them anymore. The starter motor will spin even if it has a "burnt" brush, because one of the other brushes will transmit electricity and the car will start with no problem. However, if when the starter motor stops spinning, it can land a "burnt" or faulty brush, so the next time you try to start the engine, there will be no electrical current transmitted to the engine. Sometimes, repeatedly turning the key may "bump" the starter past the bad spot and get the car's engine to start.
Why does a car start when you jumped or boosted the battery? Because instead of the normal amount of current going to the starter, a doubling of the electrical current could "jump past" the bad brush to get the motor spinning. Once the starter is spinning, it will likely continue spinning, even when the bad brush or brushes come back around in the rotation.
You need to leave the car with them until they can duplicate the problem. If it doesn't occur every time you try to start the vehicle, it will be harder for the mechanic to narrow down the exact cause. Once they can duplicate the problem, they can run further tests and fix the correct broken part.
Because even well maintained vehicles can break down, motorists should prepare a winter survival kit. This is especially true if you are driving in rural areas, or doing much highway travel. Such a kit should include: flashlight, blankets, booster cables, warning device (flares or reflective triangle), small bag of abrasive material (sand or cat litter), cloth towel or roll of paper towels, candles & matches, a Swiss Army style knife, an ice scraper and a small shovel. You should also have a supply of high energy food, such as chocolate bars or granola bars, as well as bottled water. Keep the water in your glove compartment, to reduce chance of freezing during normal winter driving.