The Google Pixel 4a has popped up at the NCC in Taiwan, confirming the device's battery capacity. According to the listing, the Pixel 4a will have a larger battery than not only the Pixel 3a, but also the Pixel 3 and Pixel 4. Google is sticking with 18 W fast charging for its next mid-range smartphone, though.
https://www.notebookcheck.net/The-Google-Pixel-4a-will-have-a-larger-battery-capacity-than-the-Pixel-3a-Pixel-3-and-Pixel-4-18-W-fast-charging-remains.478975.0.html