or for less than £130 you can just buy some new controls
https://www.securitywarehouse.co.uk/catalog/intruder-alarm-c-36/security-control-panels-c-36_102/lcd-remote-keypads-c-36_102_107/scantronic-ion-keyk01-keypad-p-3776.html
https://www.securitywarehouse.co.uk/catalog/intruder-alarm-c-36/security-control-panels-c-36_102/110-input-zone-small-c-36_102_101/scantronic-ion-10-zone-alarm-control-panel-cw-keyk01-ion10k-p-5928.html
go back in time, subscribe to maintenance contract & ensure the alarm co do the routine replacement of primary batteries ?
I'd say every 3-5 years for a siren, c sized lithium things with a wiring loom,