A further thought on battery size and life...
The monthly system self-test described in the data sheet is declared as having a total duration of 5 seconds (unchanged between unit types), elsewhere the data sheet states "Enhanced ... and self test".
There is a merit in keeping the outside observable maintenance procedures unchanged, to eliminate possible adverse risks of forward and backwards compatibility.
A reduced battery size can be speculated, based upon a system self-test using less power per usage (month), by enhancement to the test sequences and better test result data integration.