In iOS, from the iPhone 6 onwards (and especially with iOS 11.3 or higher), Apple includes a section that shows the maximum battery capacity compared to when it was new. It also alerts you when your battery is degraded and can no longer sustain peak performance. When this happens, a message like "Battery health is significantly degraded" will usually appear, and a replacement is recommended. This indicates that, even if it's still working, your device may already be experiencing battery life and performance issues. Apple generally considers a battery to be healthy if it's at 80% or more of its original capacity. When should you be concerned on Android? While Android doesn't have a uniform indicator like iOS does, many phones and apps like Accu Battery allow you to see the actual battery capacity relative to its initial state. On models like Samsung's, a battery is considered healthy if it's close to 80%. Below that, performance and battery life can be affected.

Samsung also warns that letting the battery drop below 20% can harm its long-term lifespan and recommends keeping it above 50% if the phone won't be used for a while.

What's that threshold percentage where you should be concerned, on both systems?

Apple typically suggests replacing the battery when the health drops to 80% or below. Many users agree with that figure, with one noting that, "Apple recommends replacing it at 80%, so you still have a few months before you really need to worry." Another notes that at 78% their phone is still working fine, but is already close to the limit.

In short, if your battery is between 80% and 85%, it's still good, although you may want to plan for a change if you use your phone a lot. If it drops below 80%, you should seriously consider it, especially if you notice your device shutting down suddenly or getting hotter than usual.

As one user comments, “Lithium-ion batteries degrade the most when they are fully discharged or charged to 100%. The sweet spot is to keep it between 20% and 80% charged.” Another adds: “Apple doesn’t allow you to replace it until it reaches 79%.”

The 80% recommendation given by Apple and several Android manufacturers is not random: it’s the point at which performance starts to suffer and where a battery change really makes a difference.