Unless your Pixel 4a is from Verizon (locked), keep it.
Unlock the bootloader, then install LineageOS, MindTheGapps, and Magisk.
Once you have Magisk stabilized, install the Advanced Charging Controller, and configure it to halt charging at 80%.
That should solve your problems, and turn the updates back on. I don't think there is a way to make Google Pay work in this configuration, which is a drawback.
I can put all the URLs here if you ask.
Edit:
https://lineageos.org/
[I did not remember that Lineage hosts gapps images]
https://wiki.lineageos.org/gapps/
[IIRC, the APK is renamed to a ZIP and flashed with recovery, then name it back and install the app]
https://github.com/topjohnwu/Magisk/releases/tag/v28.1
https://magiskmanager.com/
https://github.com/VR-25/acc/releases/tag/v2023.10.16
Unlock the bootloader, then install LineageOS, MindTheGapps, and Magisk.
Once you have Magisk stabilized, install the Advanced Charging Controller, and configure it to halt charging at 80%.
That should solve your problems, and turn the updates back on. I don't think there is a way to make Google Pay work in this configuration, which is a drawback.
I can put all the URLs here if you ask.
Edit:
https://lineageos.org/
[I did not remember that Lineage hosts gapps images]
https://wiki.lineageos.org/gapps/
[IIRC, the APK is renamed to a ZIP and flashed with recovery, then name it back and install the app]
https://github.com/topjohnwu/Magisk/releases/tag/v28.1
https://magiskmanager.com/
https://github.com/VR-25/acc/releases/tag/v2023.10.16