Contents: Charging amps-time Gunk in the charging port Battery Health (replacement special for 2018) Certified lightning charging cables

At https://www.imore.com/how-clean-your-iphones-charging-port

they say to use a toothpick, because the air may just pack it in further.

Battery Life is the amount of use you get from your device's battery before it needs to be recharged. This is usually measured in hours.
Battery Life is the amount of use you get from your device's battery before it needs to be recharged. This is usually measured in hours.

Battery Lifespan is the amount of time your battery is usable before it stops being able to hold a charge long enough to power your device. This is usually measured in years.

Battery charge holding capacity:

Battery Lifespan is the amount of time your battery is usable before it stops being able to hold a charge long enough to power your device. This is usually measured in years. At iPhone Battery and Performance - Apple Support - Apr., 2018 they say,
A normal battery is designed to retain up to 80% of its original capacity at 500 complete charge cycles when operating under normal conditions.
My iPhone 7 Plus still had 88% of maximum capacity after 17 months with a charge about every day; Thats 517 charge cycles.

The one-year warranty includes service coverage.

As lithium-ion batteries chemically age, the amount of charge they can hold diminishes, resulting in shorter amounts of time before a device needs to be recharged. In addition, a battery's ability to deliver maximum instantaneous performance, or "peak power," may decrease. A battery's impedance can increase if a battery has a higher chemical age, resulting in reduced voltage and power output. A battery’s impedance will temporarily increase at a low state of charge and in a cold temperature environment also.

On iPhones 6 or later with iOS 11.3 and greater under settings > battery there is "Battery Health (Beta)"

Excellent	Battery can hold its full capacity
Good	Battery can hold between 85% and 99% of its original capacity
Average	Battery can hold between 70% and 84% of its original capacity
Poor	Battery can hold less than 70% of original capacity.
        Consider replacing your battery.

Your iPhone may shut down if battery performance is low. with iOS 11.3 it will automatically enable "Performance throttling" in iPhone 6 and 7s to slow down the CPU and avoid shut downs. You can disable this in Settings > Battery > Battery Health see https://9to5mac.com/2018/03/30/how-to-check-battery-health-and-disable-iphone-battery-performance-throttling-in-ios-11-3/ and iPhone Battery and Performance - Apple Support - Apr., 2018

This can result in :
Longer app launch times
Lower frame rates when scrolling
...

Lightning Connector

iPhone 5c and 5s and new iPads have "lightning" connectors for charging; One end is a standard USB connector and the other is a proprietary connector.
Only some versions of 3rd party lightning connectors authorized by Apple will work.
The Apple lightning cable and authorized 3rd party cables have a chip in them.
A guy at the Apple Store told me that you can overcharge your phone if you don't have the chip, but I couldn't find any confirmation of this.
It appears it is just a way for Apple to make more money by charging 3rd parties for the chip.
Without the chip you may get a message saying the cable is not authorized and may not work properly. See iOS 7 now blocking some third-party Lightning cables | 9to5Mac

Work around at iPhoneHacks.com
1. with phone on plug cable into wall or laptop
2. see message above
3. press and hold power button
4. turn phone off
5. phone will cycle back on automatically
6. lock screen will show warning message but this time the phone will be charging
7. unlock phone and it will still charge.

I also had problems with some USB power supplies. A 1 amp belkin (120 V) and a .750 amp Belkin (12 V) did not indicate that they were charging my iPhone 5s with iOS 7 and the cable supplied by apple. But they were; The percent charged kept going up very slowly.
A 2 amp ASUS worked as did plugging into my PowerBook. It also worked with my HyperMac external power supply.

3rd party lightning charging cable

The Apple store told me certified lightning cables have a chip to avoid over charging. Other cables can damage your battery. StackExchange.com says there is no evidence of this.

However there are many Apple MFi ("Made for iPhone/iPod/iPad") certified cables. These will be more expensive than other non-Apple cables, but they have been approved by Apple and should not damage your device.

On amazon you can search for https://www.amazon.com/s/?ie=UTF8&keywords=mfi+certified+apple+lightning+cable

Links: