Question: can a battery charger be used to jumpstart a car

Answer: Yes, Motorists and service garages often have portable battery chargers operated from AC power. Very small ``trickle'' chargers are intended only to maintain a charge on a parked or stored vehicle, but larger chargers can put enough charge into a battery to allow a start within a few minutes. Battery chargers may be strictly manual, or may include controls for time and charging voltage. Battery chargers that apply high voltage (for example, more than 14.4 volts on a 12 volt nominal system) will result in emission of hydrogen gas from the battery, which may damage it or create an explosion risk. A battery may be recharged without removal from the vehicle, although in a typical roadside situation no convenient source of power may be nearby.