I thought I posted a suggestion to your thread earlier but do not see it. You might want to mention it to you mechanic. Just in case your choice of course. Are you positive your glow plug circuit is not staying on or the relay is latching (sticking on)for some reason until battery is low enough to let circuit disengage. You seem pretty confident your battery is good. The alternator in general seems good although I would have put a meter on an adapter from the cigarette lighter and monitored the voltage for a drive and return to verify the alternator and charge wiring plus the grounds. If voltage stayed above 13.5 except at idle you know then that alternator is delivering enough current and the wiring is good. That current is going somewhere. Best test for the glow plugs is to cycle them and check with meter to see if they are still on. The draw would be about all your electrical system would tolerate and after you turned car off discharge may continue until batery is very low and relay will unlatch. Could very well be intermittent as well but easy to rule out. Just a thought and probably wrong. Found my missing post. Saw your name and remembered your problem and posted there. Feel stupid but thats nothing new.