Sometimes, the battery has drained down so low that you are in the single-digit voltage, or even 0 Volts. In times like these, a jump start will not be sufficient to start your car. This is because portable jump starters will have a built-in safety that won’t enable the jump starter if it doesn’t sense enough voltage on the battery that it’s connected to. Using a trickle charger also will not likely work because trickle chargers work only if your car’s battery still has sufficient voltage to start out with.