Why mi iPhone battery health is low

Unfortunately, nowadays batteries are consumed parts, which means that they'll degrade even without usage (but much slower rather active usage though)

Here's some useful advices how to extend battery life:

– use original or really decent power bricks/cables

– charge the device whenever it's possible

– don't leave on the charger for a long period of time (yeah battery controllers, smart enough bla-bla but it is easier to avoid problems rather beat them up)

– DO NOT overheat your device, e.g avoid situations when the device subject to a sudden temperature drops (it's serious, common batteries (li-poly mostly) would degrade quickly)

– stay away from el.interference and strong magnetic fields

And sure thing to use original or flawless batteries

Rechargeable batteries are consumables. No matter what you do (or don't do), they will eventually lose capacity. On average, an iPhone battery loses about 1% capacity a month. What is your battery capacity? How old is your phone? Or, if you've ever had the battery replaced, how long ago was that?

Ptaxey wrote:

Unfortunately, nowadays batteries are consumed parts, which means that they'll degrade even without usage (but much slower rather active usage though)

Batteries have always been consumables.

– don't leave on the charger for a long period of time (yeah battery controllers, smart enough bla-bla but it is easier to avoid problems rather beat them up)

Apple doesn't advise this.

See here for advice on charging batteries:

When to charge your iPhone or iPad - Apple Community