What kind of alarm are you running mate? Any additional items, and tested after a good while having not opened doors or having interior lights on? 300mA is probably at the very very high end of being ok if it has been left for a while.
Would be common enough a couple of minutes after unlocking or locking the car
I had just unlocked the car, probably 2 minutes earlier. Then did it again 2 minutes after locking (since i had to keep the alarm switch under the bonnet held down manually.
So it will drop a little after that.
I am only testing because I had to keep topping my newish battery up with the charger after 4 days of not using it, so I took it back and they said it had low gravity and they put it on an overnight charge. They leant me a battery (although it was dated 2004) while doing this which suffered the same symptoms. So I presumed it must be the car.
Now however they have given me my battery back which they tested as being all ok after charging and although the longest I have left it so far is 2 days it is starting stronger than it has for a while. So I may be worrying over nothing and might have just had bad luck twice with the batterys