[shorod]

Welcome to the forum!

Have you made sure the battery cables are clean and tight? Not just by looking at them, but actually pull them from the battery and make sure there is no build-up of corrosion between the terminal and battery.

Since it's a 2003, I would doubt that it has temporary (bolt-on) battery cable ends, but if it does, throw them away and install molded cables by application.

Do the headlights work if you turn them on when it seems there is no battery power? What is the battery voltage across the terminals when the car seems to have lost all power? How about the voltage at this time between battery positive and car chassis?

Are there any environmental or operational conditions that seem to cause this problem to occur consistently (ie: after a rain, after driving the car for more than 5 miles, etc.)?

-Rod