For this topic, videos and other graphics rule. No point in posting any of these three articles. If you’re interested, go to the link.
For a teardown measuring capacity of the Apple Magsafe Battery Pack, read:
https://arstechnica.com/?p=1782561
For a comprehensive review of the Apple Magsafe Battery Pack, read:
It’s worth reading for the info, but this quotation alone is worth reading:
“A battery is not eternal. Given the volume and capacity that it has, an iPhone battery’s overall life is generally measured in years. User behavior can cut this down, and Apple has taken steps to help with this, and minimize the accumulation of minor damages over time.
When the battery is connected to an iPhone, it will charge your iPhone up to 90 percent before stopping, using Apple’s smart battery charging algorithm. The final stretch from 90% to 100% takes a disproportionate toll on overall battery longevity versus the rest of the charge, so Apple keeps you topped off at 90% rather than letting your battery take the hit.
You can go past this 90% if you’d like by going into Control Center and manually allowing it.
In a further extension of battery maintenance, if the iPhone internal temperature is high, the battery will cut off charting when the phone hits 80%. High temperatures are also harmful to lithium batteries, so battery charging is halted a bit earlier to prevent any further damage.”
And finally, (less expensive) alternatives:
https://appleinsider.com/articles/21/07/13/apples-magsafe-battery-pack-is-official-here-are-some-alternatives [too many graphics to post]
Abycats' Thoughts 