Daox, Have you tried or know of anyone who has tried one of these PowerStream DC-DC converters?
12 volt DC/DC converters regulator from 100 to 700 Watts.
I'm considering trying one of these out.
Also, what is the power draw of your alternator with the field and regulator energized, but the engine not running?
My alternator has a 0.2 volt and 5.45 amp draw when energized (key in run position), but not charging.
At least with my Focus, this seems to be a significant draw of power even when not charging. I haven't separated the regulator power from the field because it's not so simple in this particular design so I'm unsure which is causing the big drain. I'm likely to just swap to a different alternator type before getting that far though.