ML500 Battery Dies After 2 Days Of Sitting

[zeronero]

My friend's 2003 ML500 has an issue that he can't resolve himself, the battery dies if the vehicle isn't driven every 2 days or so. He says he's checked everything and has had the dealer check it out but so far nothing has come up. He said the went through the vehicle thoroughly checking everywhere that a light could be left on or a sensor could still be left on and has had no luck. He's out of the country at the moment and I told him I'd take a look at it. I figured here is a good place to start since this might be common theme among ML owners.