Can I replace my iPhone 12 mini battery?

You can have your battery replaced. Apple has a cost estimator if you were to take it to an Apple Store for service. iPhone Battery Repair & Replacement gives the figure of US$89

There is further information on that linked page.

Yes, you can replace the battery on your iPhone 12 mini. However, it is recommended that you have it done by a certified technician or at an Apple Store to ensure a proper and safe replacement.

If you are experiencing significant battery degradation on your iPhone 12 mini, it's essential to check if there are any software or hardware issues causing the problem before opting for a battery replacement.