u/Mother_Bed_9889

I came across this image on internet and wondering since then what is it. Can you explain it?

This is my iPhone 12 pro max. I purchased it on Jan’21.
My device is running fine but the battery backup is around 3-4 hours.
Experienced people in the Sub please share your thoughts about what should I do?
Should I go for new device or
Replace the battery and use the same device or
Go for a second hand device or
Anything else you can recommend?