iPhone Charging

Hello,

It will mostly continue to charge almost indefinitely. However, it won't hold a charge very long when it gets old.

Check the battery health as noted here: iPhone Battery and Performance

If it won't charge at all, check the charging port for lint or other debris and see this:

If your iPhone, iPad, or iPod touch won‘t charge

For more discussion, see this:

When to charge your iPhone or iPad

Good luck.

Apple has a nominal rating for iPhone batteries since (I think) the iPhone 5 of 500 charge-discharge cycles before an expected decline to 80% of original battery capacity. But every battery and situation is different, and there are all these little things that affect how long a battery lasts that don't necessarily fit into Apple's simplifications of battery use as "full cycles". Apple's rating is a simplification that most people can understand even if it's not that precise. Apple encourages uses to use "Optimized Charging" which may or may not delay charging at 80% until the morning, on the premise that limiting the time that it's above 80% is good for long term battery life.

There's no set limit, although often when batteries start to really degrade they can do it suddenly. I have well over 500 cycles on my iPhone 7 battery and it's still reporting 92% battery health, although I think it's due for an update by now. I don't know how long it's going to last. Some batteries will die quickly to the point where the charging circuits won't charge the battery for safety reasons. I've seen it happen a few times.