How to bring iPhone battery capacity back to 100%?

You cannot bring a battery back to 100% unless you replace with a new battery. Battery Health is an inexact figure that varies with usage. The typical Apple Battery lasts about 2 years. You need not worry until your Battery Health figure goes down to 80%, at which time you will need to make an appointment at the nearest Apple Store for Battery Replacement. Check this link...

https://www.apple.com/batteries/maximizing-performance/

Hi Brittnu,

All batteries tend to degrade over time. You can replace your used battery to a new one which will make your capacity go back to 100. Please reference this article from apple, this may shed some more light on the topic. https://support.apple.com/en-us/HT208387

Cheers!

Batteries age with time and their is no way to rejuvenate them other than replacing them. For more info, see the 'Your battery's maximum capacity' section in:

iPhone Battery and Performance - Apple Support

or

When to charge your iPhone or iPad - Apple Community

"keep in mind that batteries are "consumables". Their capacity starts dropping the day they come off the assembly line. Battery life is determined primarily by "full charge cycles" - A full charge cycle is 0% to 100%, or any combination that adds up to 100%, such as 50% to 100% or 30% to 80% twice, 80% to 100% 5 times, etc. The battery will gradually lose capacity, and is rated to remain above 80% capacity (that's total capacity, not charge level) for 500 full charge cycles for an iPhone (1,000 for an iPad). For most people this will be around 2 years for the iPhone. Apple will replace the battery for a reasonable fee (currently $49 US for older phones, $69 for iPhone X and later) if it goes below 80% after the original 1 year warranty or AppleCare+ warranty period. Within the warranty the replacement is free."

zakir_49 wrote:

All batteries tend to degrade over time.

Perhaps it's pedantic but, they don't "tend" to degrade over time. Batteries will, without fail, degrade over time. It's inevitable.

Picky, picky, picky, ...

Don't want to give the OP false hope! ;-)