You upgraded too soon. It is practically the same phone. If it was a base 13 you would feel the difference more.

https://preview.redd.it/icl1ss4cgm2c1.jpeg?width=3024&format=pjpg&auto=webp&s=ff0aa7ddee960a607f6905608dc3b2348701e3bf

10 seconds, handheld, iPhone 12 (the base model)

Google maps, chrome, gmail

A friend of mine used to work at a repair shop. He told me that if the phone is used with a cracked back glass, small pieces of glass penetrate the battery, causing the battery to swell up. Same thing happens when the back glass is replaced sloppily.