My 13 mini is also not great on battery. I've been debating ordering an iFixit battery and doing the swap, but in the past I've felt it was kind of mixed results from that. I don't think those batteries are newly manufactured units, but rather leftovers from the original production line that have been sitting on the shelf for 2-3 years. So although they'll be an improvement over one that's been through 1-2k cycles, they won't be like it was when it was brand new.

For now I'm just making do with having a power bank in my bag when I'm out and about.