Is that worth doing? There’s nothing wrong with it at the moment and I’m not sure what might improve.
I don’t plan to work on it 
Its a pity that it still require such an amount of work. My Battery is dying from 18% to 61% Degradation in the last days if i can trust the BMS (Usage App from Storeman). You know theres this weird Battery-Level-Stall on this Port, my hope is that a newer kernel fix it. I have received a new Battery from Sony, sadly produced 20W47, so week 47 (End November) of 2020. Our Sony-Sparepart-Dealer told me Sony has stopped Battery production for the xz2 compact. I had ordered the C2 already but like my xz2 compact too much to let it go.
That Battery had far more Charge-Cycles like 86, but maybe not completely (0%-100% and 100%->0%)
I changed the battery to mine and works just fine. Never noticed extremely weird things with the battery.
Maybe its better to stay on Kernel 4.14 with this port because:
I successfully changed the battery. The charge cycles were reset, but it still shows the available capacity and degradation from the old battery. I tried to fully charge it to 100% and waited until the current was down to 14 mA, but I never received the ‘Battery completely charged’ message from SailfishOS. I also let it drain down to 2% when SFOS shuts down. Is there any experience with this unit regarding when the BMS will calculate the correct available capacity, or is there some kind of reset mechanism?
Added 06.09.2024:
Reset the Charge-Full-Value by Hand after Battery-Change doesn´t work:
[defaultuser@XperiaXZ2Compact ~]$ cat /sys/class/power_supply/battery/charge_full
1113000
[defaultuser@XperiaXZ2Compact ~]$ cat /sys/class/power_supply/battery/charge_full_design
2899000
[root@XperiaXZ2Compact defaultuser]# echo 2899000 > /sys/class/power_supply/battery/charge_full
bash: can’t create /sys/class/power_supply/battery/charge_full: Permission denied
After 33 charging-cycles the BMS doesn’t recognize the new Battery and still show the values of the old one. Conclusion is, the measuring of the capacity works only downwards and there seem to be a missing reset-mechanism in AOSP at least for this Hardware (Sony XZ2 Compact).
When receiving my C2, i will do some tests with the XZ2c regarding BMS-Reset and will share my knownledge here, how to do it.
Edit: Added 12.11.2024
Ok, so SailfishOS and/or AOSP seems to save this Data outside of the scope of Stock-Android on this Sony XZ2 Compact Device.
I first try to reflash verndor.img and dtbo.img to reset this → nothing changed
Then i flash Stock-Android on it and make some charge/discharges, see AccuBattery-Screenshot below, Battery-Capacity is calculated correctly.
At last i flashed back SFOS and it still shows the old Values!?!?
And the Emma-Tool doesn´t offer Battery-Recalibration after flashing Stock-Android to it.