I’ve had the mini for a few months now and have no problem getting thru a full day, meaning 12-15 hrs, depending on what I do on a particular day. There have been some days I’m using my phone a lot and need to charge in the middle of the day. I do also carry a MagSafe battery just in case I’m out and need a battery bump.
I was previously a 12 Pro user and between that and the mini, the battery life isn’t bad at all. Yes it’s not as long as the 12P but obviously to be expected.