Bugger me I'm getting old
When I first discovered t'interwebs a username containing 'red dwarf' usually denoted a spotty 15 year old herbert
now its the mark of a penniless pensioner
but seriously, no really, I agree - replacing with battery devices is a backwards step.
Even nest ones as they are designed to be binned in ten years, they simply refuse to work past their tenth anniversary.
If you think you have the skills to reprog the unit, which you may have, or not, who knows, whats stopping you replacing the smokes?
You'll actually find 12v smoke detectors CHEAPER than decent quality mains+battery Aicos for a start, and the wiring and panel area already in place, so...