2008 Mercedes Benz ML350 Car wont' start - Fuel

How did you come up with a fuel problem causing an electrical problem? If the engine won't crank, you haven't even gotten to the point where fuel is needed. The first thing to suspect is the battery. How bright are the head lights? What happens to them when you try to crank the engine? If you have a digital voltmeter, measure the battery voltage. It must be 12.6 volts. If you find it's closer to 12.2 volts, it's okay but discharged. Charge it at a slow rate for an hour, then try cranking the engine. If it's around 11 volts, it has a shorted cell and must be replaced.