VT Commodore draining brand new battery?

Hi, I have a 98 VT Acclaim. Have had it 6 years and hasnt missed a beat. Just recently the air bag light has started coming on when the car starts and not turning off until it stops. Not sure if it is related, but something is completely draining my battery. It is draining to the point where even the remote key wont unlock it because it is too flat. i have had my radio disconnected, replaced the battery (twice), put new battery terminals on it, put a new alternator regulator on (at my brother in laws insistance!!). I have had a mechanic look at it and he tells me the battery is charging fine thru the alternator and he can see no problem. (No lights satying on - glove box/boot) I am struggling thru with no car cos I cant afford to send it to an auto electrician (I am a single mother). Any ideas on what this could be would be greatly appreciated. I have a great mate who is very mechanically minded, but he too has no idea. Thanks in advance