my battery percentage is reducing even when not in use.But my battery health is 100

Hello ~ Not normal for an iPhone 7 to show 100% battery health. My iPhone 12 mini is at 85% and will be replaced when it hits 80%. You may need to have that checked.

Genius Bar Reservation and Apple Support Options - Apple

~Katana-San~

Because there is never a time that an iPhone isn’t doing something. It periodically registers with the cellular network so it can find you for incoming calls, it receives and processes notifications from any apps that you subscribe to, it receives and indexes emails sent to you, it updates several apps such as weather and stocks (and many 3rd party apps) and many other syncing functions. All of these activities use energy.

No, it is perfectly normal for any battery powered communications device to use energy when you are not actively using it, as I explained. If you replaced the battery the new battery would do exactly the same thing. When are you seeing this loss of state of charge, and how much is it losing in how much time?

There is a very rare failure mode of some batteries called “self discharge”. You can test for this yourself. Charge to 100%, then unplug and turn off the phone completely (don’t just put it to sleep) by holding the SIDE button until “slide to power off” appears and do so. Leave the phone off for several hours. When you turn it back on the battery state of charge should still be 100% or very close (e.g., 98-99%).

Hello ~ Is that your original battery? If not who replaced it?

~Katana-San~

Hello ~ Get it checked out as Apple will let you know and make a recommendation for you.

~Katana-San~