Veritas 8C back up battery replacement?

We had a power cut yesterday and the alarm was going until power was restored. Can I change the back up battery myself and if so, is it located in the alarm panel or the box on the wall outside the house (the one that has the flashing light) once the power was restored I could cancel the alarm but I have been told the reason it kept ringing when there was no power was a battery had run out. Thank you.