This has been stated here over and over and over again. The Opus 150W ALWAYS powers the +5VSB rail. Depending on your motherboard and peripherals, you could end up drawing upward of 100mA on your supply lines. This WILL drain your battery. There is a simple work around to this problem posted in the forums.

Here are the measurements you asked for posted over a year ago.

http://www.mp3car.com/vbulletin/show...0&postcount=18

BTW, to be accurate, even though the M1-ATX does allow you to shutdown the +5VSB rail also, it will still consume some power (a few mA at most) though this amount is likely to be substantially less than your car already draws while off.