Hi Jeff, thanks for your reply. I have an iPhone 12 mini, iOS 26.2 now, I am the original owner though it is a refurbished phone, and my battery health is 75%.
To give some more information (and also as a rebuttal to a previous comment): I am currently doing research and use my phone for data collection. It is always 100% charged when I start at 7am, and would get to 20-30% when it's time to stop at 12:00. After the Liquid Glass update, I did not make it until 12:00 while I used my phone in the same way, and actually less, because by 9am I noticed how much the battery already had drained (under 60%). Same story for the afternoon data session.
It's an old phone and I know it needs a new battery or replacement at some point, but the fact that the upgrade is draining the life out of it (there is no other explanation I can think of) is a bummer, to say the least. Especially because I can't simply buy a new iPhone or battery at this point, only when I will return from my fieldwork.