iPhone 15 battery draining fast

Start here:

Batteries - Maximizing Performance - Apple

“Battery life” is the amount of time your device runs before it needs to be recharged. “Battery lifespan” is the amount of time your battery lasts until it needs to be replaced.

"With iOS, you can easily manage your device’s battery life, because you can see the proportion of your battery used by each app (unless the device is charging). To view your usage, go to Settings > Battery."

About the battery usage on your iPhone, iPad, and iPod touch --> About the battery usage on your iPhone, iPad, and iPod touch - Apple Support

and Check the iPhone battery health and usage - Apple Support

I had an iPhone pro 15 that drained battery much faster than the iPhone 13 Pro it was replacing.

Drain was higher all the time but I noticed at night the drain was happening while findmy was active. I could see this by selecting the section of battery use and that nothing else was showing except findmy. battery was dropping 40% or more overnight while not in use.

I returned the phone within the refund period and all is back to normal with the older iPhone 13 Pro so seems to be specific to the newer model.

if I’d missed the return window I would probably have just turned the phone off each night. But appreciate that won’t help battery drain during the day. I think findmy activity might be at the root of the problem so might be worth experimenting with that eg what happens if you turn off all the other Apple devices apart from iPhone, to see if that makes any difference. Findmy is an important feature though so turning off to solve battery drain is problematic.

I bought 15 pro max two months ago. It runs out of charge after a whole day of use, I put it on charge at night and then I can walk all day. If you turn off the functions in the background, it will last a little longer. Definitely 14 held the charge longer, it lasted for 1.5-2 days. I hope this will be fixed in the new iPhone 16.