No, you cannot start a car with a completely dead or missing battery. The battery is essential for providing the initial burst of power to crank the engine and run the vehicle's essential electronics, like the fuel pump and engine control unit (ECU). Even if the alternator is responsible for generating electricity while the engine runs, it cannot produce the massive amperage required for the starter motor to turn the engine over from a standstill.
However, there are two methods that can work if the battery has a small amount of residual charge left. The most common solution is a jump-start. Using jumper cables connected to a donor vehicle's good battery provides the necessary power to crank your engine. Once started, your car's alternator will take over and begin recharging the weak battery.
The second method, push-starting (or bump-starting), is only viable for vehicles with a manual transmission. This technique uses the car's own momentum. With the ignition on and the car in second gear (clutch depressed), it's pushed or allowed to roll down a hill. Once speed is gained, quickly releasing the clutch engages the transmission to the engine, forcibly turning it over to start. This method bypasses the starter motor entirely but still requires minimal battery power to run the ECU and fuel injection system.
For cars with automatic transmissions, push-starting is not possible because the hydraulic torque converter does not create a direct mechanical link between the wheels and the engine. If your battery is repeatedly dying, the underlying issue could be a failing alternator, a parasitic drain, or simply an old battery that needs replacement.
