Urgent help needed with battery disconnection

[CBlack1105]

This is actually a 330 question (but I also have an X5, so I thought you guys might give me a break!).

I need to disconnect the battery because I am about to leave the 330 for a few weeks but as soon as I disconnect the negative terminal (as instructed by the manual), the alarm starts to beep (it doesn't actually go off, just beeps) for about 20 seconds, then waits for a bit, then beeps for another 20 seconds, etc.

Is there any way I can disconnect without the alarm beeping - I presume this is the alarm giving me a warning (thanks, I don't need one, I know I disconnected the battery).

Also, do I need to disconnect the +ve terminal as well as -ve?

Thanks