If you can reset your system after it goes into full alarm, by simply entering your user code, then it's set up for user, so in theory you shouldn't encounter any problems resetting the system following a battery change.
It's important for your own safety to remove mains power before you remove the panel's cover ( two screws at the bottom corners),the lid will hinge up and can be removed.
Don't worry about the tamper alarm,replace with the same amp hour rated battery, observing correct polarity on connection, ( red+ positive )&( black - negative ).
I would expect the outside bell to sound off when you remove the battery," don't panic " carry on and fit new battery, cover back on, reastablish mains power.
Pop your user code in twice to reset the system and the system should return to day mode,with the fault codes
cleared,if for any reason you can't reset then enter ( 9090) to enter engineering, then exit engineering mode.
Note: the engineering code may have been changed by the installer.
any problems get back and we will try and help,
good luck and remember power off first, be safe :)
e manno
September 2012