backup left on site is one option, but its like sage, word etc its up to the client to backup unless they are paying for a managed backup solution off site etc. Also should the backup be encrypted if your taking it and its found inside the pc etc
thats not a wiring issue then, maybe programming, how are you testing it, ie what are you doing to cause a full alarm. What happened when you did the bell test?
Id say every 5 years is fine. Better to replace before panels report it to prevent damage but modern panels seem to do better with failed battery's than the old dumb stuff