I finally opted out of the 12L Beta.
A warning for those who may also go back to the stable version, it wipes your device clean, and it needs to be set up again as a new device.
The battery life of the 12L was very poor for me. Neither AccuBattery nor the system's battery identified "rogue" apps as some here suggested.
It is definitely the Mobile Network. Mobile Network drains between 35% and 80% every hour, and this was before and after I reset the network and forced network reactivation.
My feeling is that a lot of those who claim great battery life have disabled 5G. In my opinion, the phone should be expected to work on 5G, as advertized. I understand that 12L is a beta, but the fact is, it's not well optimized, at least not yet, for 5G.
I am back on the stable version, after spending a couple of hours setting up the phone again, and my battery is back to normal, which is not nearly as good as iPhone 13 Pro Max, but at least gets me through the day.
This is just to warn those who might be tempted to try the 12L beta, and care about 5G.