A jump starter is an auto power tool that boosts a car battery if and when the battery power has depleted to a point that there's not enough power to start a car. Much like a battery charger for cars - they have a specific function and are useful to have around.
They come in a variety of makes, models and prices - the underlying principle being that they all provide the power required to turn the engine over, which in turn allows the alternator to recharge the depleted battery.
The five best jump starters are featured below. They're all highly rated product by previous purchasers, offer good value for money and of course they're the best selling models on the market.