On top of the many new features Apple had released with regards to iOS 13, it looks like another addition Apple has given is a feature that will make iPhones last longer. While Apple continues to support older iPhone models, it's usually the battery of the older models that spells its end.
In order to increase the battery lifespan of iPhones, Apple has added a new feature in the upcoming iOS 13 update called the "Optimised battery charging" feature. This latest feature is meant to help "slow the rate of battery ageing" and will "reduce the time iPhone spends fully charged".
In other words, your iPhone battery will not be fully charged all the time. So even if you keep it charged overnight, the battery won't charge beyond 80% if it is not necessary. But what do they mean by necessary and how will they decide that? Apple explained that, "The iPhone learns from your daily charging routine so it can wait to finish charging past 80% until you need to use it."
For those unaware, charging a battery up to 100% is not good for its lifespan. Experts have suggested that to ensure your batteries last in the long run, it's better to charge the battery to 80% and drain till 20% before recharging it again. Charging the battery to 100% and letting it drain until 0% will affect the battery's lifespan and would be visible after two years or so.
This update will be available for free for iPhone 6s and later devices. So if you're using the iPhone 6 and below, tough luck.