A parasitic battery drain is when there is an electrical current running through the car’s system even when the engine isn’t running. To check for this, you can use your multimeter to measure the voltage of your battery when the engine isn’t running. The reading should be 12.4-12.7 volts or higher. If it drops below that, then you may have a problem with your car’s electrical system such as a short circuit or a faulty component that needs to be replaced to prevent further damage to your vehicle's battery.