How batteries age
iPhone batteries just like all rechargeable batteries are consumable parts that become less effective as they chemically age and their ability to hold a charge diminishes. Although the number of times a battery has been charged (known as a battery cycle) can affect the life of a battery this is not the only factor in this chemical ageing process. Device use affects the performance of a battery over its lifespan, for example in hot environments a battery may age faster. These characteristics of battery chemistry are common to all lithium-ion batteries.
A chemically aged battery becomes less capable of delivering peak energy loads, especially at a lower state of charge. This can result in your device unexpectedly powering off to prevent damage due to low voltage. With the introduction of iOS 10.2.1 some time ago a new power management feature was introduced which to some extent throttles devices who's batteries can no longer deliver peak power. This "throttling" can cause longer app launch times and general lag across the iOS system. This can be resolved by fitting a new battery, at which point the system will no longer throttle.
Earlier this year Apple introduced a feature to check your current battery health within an option on Settings. Here you can see the current battery capacity but more importantly if the "throttling" power management has been applied due to an unexpected shutdown. You will see a message as shown below if this is the case:
Typically we recommend batteries be changed at around 80% capacity however this isn't always the case. If you have experienced an unexpected shutdown even above 80% capacity we'd recommend a battery replacement as the "throttling" power management will have been applied.
To give an idea of what kind of performance decrease a consumed battery results in we can run a CPU test on Geekbench. Geekbench allows you to benchmark CPU's and check performance. An iPhone 6s with a new battery results in the following Geekbench scores:
However a 20% consumed battery would lower these scores to
These scores show a 45% decrease in performance at best. This would result in a significant slow down of system performance and across all tasks on iOS.
Getting a replacement battery
Here at iPatch we have been offering battery replacements for £25 for selected models which result in system throttling. However the offer ends on 31st December so there isn't long to take advantage of this offer.
You can view the pricing of battery replacements and other repairs here.
A replacement takes no more than 20 minutes to complete and can give an older device a big performance upgrade.