You can check your battery health by going to Settings > Battery > Battery Health. The most important indicator there is the Maximum Capacity percentage. Mine currently says 88%, as you can see in the screenshot below. Yours may say something like 85% or 90%. You should check your Maximum Capacity when your phone is fully charged because it gives the most accurate number. The more you use your iPhone, the smaller this percentage will get. When you purchase your iPhone as a brand new device, this number will be 100% or something only slightly less than this. The Maximum Capacity is the biggest indicator as to when you need to change your battery.
Your battery ages but its age is not measured in calendar time like it is as we age. The more you use your iPhone, the older your battery gets.
What does Maximum Capacity percentage mean?
Essentially, this percentage indicates how many times your iPhone has gone through recharge cycles. So what is a charge cycle? A charge cycle does not mean that you charged your iPhone from 0% to 100%. Here is what Apple says:
Apple lithium-ion batteries work in charge cycles. You complete one charge cycle when you’ve used (discharged) an amount that equals 100% of your battery’s capacity — but not necessarily all from one charge. For instance, you might use 75% of your battery’s capacity one day, then recharge it fully overnight. If you use 25% the next day, you will have discharged a total of 100%, and the two days will add up to one charge cycle. It could take several days to complete a cycle.https://www.apple.com/batteries/why-lithium-ion/
Apple further says that an iPhone that has gone through 500 cycles should still retain about 80% of its original capacity. I should mention that this does not mean that after 500 charge cycles, your phone will not be usable. However, you will likely have battery problems. Your phone may slow down, or may shut itself off unexpectedly.
Apple shows how many times you have had charge cycles in percentage instead of showing the actual number. From the Maximum Capacity percentage, we cannot know for sure how many times your phone has been recharged, but we can guess. If the number is closer to 80%, your recharge cycle is close to 500. Or, if your Maximum Capacity is at 99%, your phone has had only a few charge cycles.
When to change the battery
Apple says you need a replacement if you see your Maximum Capacity around 80% or lower.
Apple may replace your battery for free if you are covered under warranty or AppleCare+. If not, Apple can replace your battery for $69 for most models:
- iPhone X and later: $69
- iPhone SE and other models: $49
You may have Apple’s limited warranty or AppleCare+. In terms of battery, here is what they do:
- Limited warranty: This is a year-long warranty that starts after the purchase. This is the basic warranty included with your purchase automatically. If your battery health level reaches 80% or less within a year, the warranty covers the battery replacement. You can check to see if you are still covered under warranty.
- AppleCare+: This can be purchased within 60 days of your iPhone purchase, or you can buy it with your new iPhone at the time of the purchase. It provides up to 3 years of coverage. You can check to see if you have an active AppleCare+ warranty.
How to replace the battery
If your peak performance is at less than 80%, there are three ways to replace the battery:
- You can mail your iPhone to Apple. If you choose this option, there will be a shipping cost (in the USA, it is $6.95) regardless of warranty status. Apple usually ships back your device within 3 to 5 days.
- Make an appointment and take it to an Apple Store. They will probably replace it while you are there. It is usually a quick process.
- If you do not want to mail it or if there isn’t an Apple Store around, the third option is to take it to an Apple authorized service location. You can ask Apple about the store nearest you.
I did not include the information here, but there are also do-it-yourself options. Ifixit, for example, sells battery replacement kits that you can buy to do the replacement yourself, if you think you have the right skills. You should know that this can be risky and voids any Apple warranty.
Lastly, this is a different route but, you can consider a trade-in instead of replacing the battery.
This page provides more info regarding battery replacement options offered by Apple.