iPhone 12 mini running 14.8.1

All those symptoms are signs of a failing battery. Just like batteries in other objects such as flashlights, batteries in cell phones wear out with usage. She needs to make an appointment at the nearest Apple Store for Battery Replacement. It is not very expensive. And then she needs to update to the latest version of iOS so that she will be safe from all the shady folks out there. I always do an update the day it comes out and I have never had a problem with an update. For a few days after an update there will be added battery activity as the update completes.

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Any update will potentially "take a toll" on your phone's battery, but that is only a temporary situation. A lot goes on in the background, during and immediately after, updating the phone. This is normal. Not sure what you have read.

Regardless, updating is certainly your prerogative. Just be aware that each update provides new features, may have bug fixes, and add increased security that you miss out on if you decide not to. Again, your call.

I, too, have an iPhone 12 Mini. I suggest that you update as soon as possible. Updates contain important security features to keep you safe. I certainly consider safety more important than battery life. The typical Apple Battery lasts about 2 years with normal usage and is easily replaced at any Apple Store. Our 12 minis are more than 2 years old and as yet mine still has original battery. When Battery Health reaches 80%, it will be time to replace it.