can i replace a 6 volt bell box with a 12 volt bell box?

I have a itec horizon alarm but the bell has a 6 volt battery.
I want to replace it with a 12 volt box would this be easy to do or would the whole system have to be changed, i know there are tamper switches on pir's and the control box as well.
I currently have a number 7 fault which i think is from the bell box as the battery is about 20 years old and only showing 2.5 volts.
many thanks for any help.