My '99 S70 started doing the exact same thing a few months ago. I had everything checked including the alternator, and everything checked out to be good at most places. About the fifth place I visited said my alternator wasn't putting out exactly what it should. I think it was putting out exactly 12 volts...not enough to throw a dash light, but enough to drain the battery while driving. I had replaced the alternator last Feb. and it was still under warranty. I carried it back to Oreilly auto and exchanged it for a known good one and my problem has disappeared. Alternator light never came on. Who did you have check your alternator? Have another look at it if you can't find any draw on the battery when removing fuses.