@Gavaudan, thanks for the heads-up. Any chance that your current device battery life could instead be due to the modest battery life of the 4a itself and not the Calyx OS? According to this revue, weaker battery life is an issue with all the Pixels in the 4 family.
Plus, the Calyx site extols the virtues of the microG replacement for GMS including “reduces battery, memory, and CPU usage”.
https://calyxos.org/features/microg/