UK Mazda 3 Sport battery draining.

Our 2002 MX-5 used to get a flat battery if not driven regularly. Fixed 
by getting a battery conditioner.

Our 2004 3 Sport suffers from a flat battery unless it gets regular long 
journeys. Does not seem to be a problem if we turn the alarm off.

Last week the car was used for about 10 3mile trips over Monday to 
Friday. Not used over the weekend when we used our 2007 MX-5 coupé:-)

Today Monday the 3 turned over about twice with the dials and dashboard 
lights going berserk.
Just over 2 hours on a 0.6amp and it started with no problem.

Anyone any ideas?
Battery had it? Any ideas on how to test?
Alarm drain excessive?
Any other drain ideas? Only extra on the car is a multi CD player dealer 
fitted when new.
Is there a regulator that cuts the power when the voltage drops? Seems 
to go from virtually dead battery to OK to start the car with very 
little charging indeed.

We had the same problem about 6 months ago which seemed to disappear if 
we always turned the alarm off. 10 days parked at the airport was no 
problem.

Started using the alarm again when back window shattered in suspicious 
circumstances.

TIA for any ideas.