The battery health feature in settings provides information on current maximum capacity and peak performance capability, and will also inform you if your iPhone is being slowed down, whether it needs service, and will even allow you to turn off advanced power management — now called performance management — if you so choose.
If your iPhone SE, iPhone 6, iPhone 6s, or iPhone 7 had been slowed down due to prevent an unexpected shutdown, iOS 11.3 will restore it to its previous, unmanaged performance levels. Performance management will only kick back in when and if you experience another unexpected shutdown. Until then, it’s a clean slate.
Peak performance capability is the ability of your iPhone’s battery to supply adequate charge even in the face of highly demanding tasks, up to and including those that cause power spikes.
Apple shows the following messages, depending on the capability to handle peak performance:
- 100%: Your battery is currently supporting normal peak performance.
- 95%: This iPhone has experienced an unexpected shutdown because the battery was unable to deliver the necessary peak power. Performance management has been applied to help prevent this from happening again. Disable…
- 79% or less: Your battery’s health is significantly degraded. An Apple Authorized Service Provider can replace the battery to restore full performance and capacity.
- Unknown: This iPhone is unable to determine battery health. An Apple Authorized Service Provider can service the battery. More about service options…
If you disable performance management, you’ll see the following message:
This iPhone has experienced an unexpected shutdown because the battery was unable to deliver the necessary peak power. You have manually disabled performance management protections.
You can also use these settings to disable performance management… to a point. Performance management has never been completely about batteries. All processors have always been throttled to protect against heat, for example. That kind of performance management can’t be disabled — it would literally allow your iPhone to fry. So, the only performance management you can disable is the battery-related performance management Apple introduced with iOS 10.3.1.
it’ll also only stay disabled unless and until you suffer another unexpected shutdown due to a power spike your battery can’t handle. Then it’ll kick back in. You can disable it again, but it will be re-enabled every time you experience that kind of shutdown.
And as a reminder, this doesn’t affect iPhone 8, iPhone 8 Plus, or iPhone X, which use a different method to manage peak power draw, nor does it affect iPads, which have batteries so large it’s unlikely they’d ever power down in face of power spikes.