I think my iPhone is draining battery more than it should be?

I lost about 10% of battery after fully charging it after 25-30 minutes at low brightness, and connected Wi-Fi. Should i be worried? I had to resend my phone back and forth because of the same problem.

I'm not sure is what's causing the problem is it the battery or the software have you tried restoring your iphone it may work

It seems somethings wrong with your iPhone, send it to Apple after-sales service