iPhone battery health: what the percentage means and when to worry

Your iPhone says 86%. Is that good? Should you replace the battery, sell the phone, or stop worrying? Battery health is the one number every buyer, seller and repair shop looks at first, and it is easy to misread.

Here is what the percentage actually measures, how to check it on an iPhone or a Galaxy, which numbers are normal for a phone’s age, and the few habits that keep it high.

Battery health is how much charge your battery can still hold compared with when it was new. Above 90% is excellent, 80 to 89% is normal wear, and below 80% is the point where most people notice shorter days and where replacing the battery starts to make sense. You can check it in Settings › Battery › Battery Health.

What the percentage means

A lithium-ion battery slowly loses capacity as it ages. When your iPhone shows 86% Maximum Capacity, the battery can hold about 86% of the charge it held on day one. The phone still charges to 100% on screen; there is simply less energy behind that 100%.

Two things wear it down: charge cycles and time and temperature. One cycle is 100% of capacity used, whether in one go or spread over several days (two days at 50% each make one cycle). Heat speeds up the chemical aging even when the phone is barely used.

As capacity drops, you get shorter days and, on an older battery, the phone can manage peak performance to avoid unexpected shutdowns. That is why a tired battery can make an otherwise fast iPhone feel slower.

How to check it

On an iPhone

• Open Settings › Battery › Battery Health (on iPhone 14 and earlier, it may read Battery Health & Charging).
• Look at Maximum Capacity. That percentage is what everyone means by battery health.
• On iPhone 15 and later, tap the Battery Health readout to see the cycle count, the manufacture date and the date of first use.

On a Samsung Galaxy

• On many recent Galaxy phones, go to Settings › Battery and scroll to Battery information for the health percentage and cycle count. It depends on the model, region and software version.
• If it isn’t there, open the Samsung Members app and run the battery test in Phone diagnostics. You get a rating (Normal, Weak or Bad) instead of a number.

What’s a good number?

How fast you get there depends on the model and your habits. Apple says batteries in iPhone 15 and later are designed to keep 80% of their original capacity after about 1,000 complete charge cycles under ideal conditions, and earlier models after about 500. Someone who charges once a day reaches 500 cycles in well under two years.

What actually wears a battery out

• Heat. The big one. Apple calls 16 to 22°C the comfort zone and warns that ambient temperatures above 35°C can permanently reduce capacity. A phone left on a car dashboard in July ages faster than one used every day indoors.
• Charging in a hot case. Apple notes some cases trap heat while charging. If the phone gets hot on the charger, take the case off.
• Gaming or navigation while charging. Heavy use plus charging means extra heat.
• Storing it full or empty. For a phone going in a drawer, Apple recommends leaving it at around 50%.

How to keep it high

• Leave the charging optimizations on. Optimized Battery Charging learns your routine and holds the charge at 80% until shortly before you usually unplug. Apple says turning optimizations off can increase battery wear.
• Use the charge limit on iPhone 15 and later. In Settings › Battery › Charging you can cap charging anywhere from 80% to 100%, in 5% steps. 80% is the gentlest setting if your day allows it.
• Keep it cool. Out of direct sun, off the dashboard, case off if it heats up while charging.
• Don’t stress about the details. Charging overnight, topping up during the day or using a fast charger is fine. Heat matters far more than how often you plug in.

Replace the battery, sell, or upgrade?

If the phone does everything you need and only the battery is tired, a new battery is usually the cheapest way to get another couple of years from it. In Ottawa and Gatineau, our mobile repair service can replace an iPhone battery at your home or office.

If you were planning to upgrade anyway, battery health is part of what sets your phone’s value. At Deviceli, 90% or more opens every grade, 80 to 89% still gets a Good or Fair offer, and below 80% counts as one issue. We explain it in detail in How much is my used iPhone worth in Canada?

And if you are buying used, always ask for the Maximum Capacity before you pay. A cheap phone at 79% may need a new battery right away.

How Deviceli handles batteries

Every refurbished phone in our shop has a battery at 80% health or better, checked before it is listed, and comes with a 12-month warranty and 30-day returns. When you sell to us, we check battery health at inspection, so you don’t need to know your number before you ask for an offer.

The bottom line

Battery health is a simple measure of how much charge your battery still holds. Above 90% is great, the 80s are normal, and below 80% is when replacing or moving on makes sense. Keep the phone cool, leave Apple’s charging optimizations on, and the number will drop slowly.

Frequently asked questions

What is a good battery health for a used iPhone?

90% or more is excellent, 85 to 89% is normal for a phone that is a year or two old, and 80% is the minimum most reputable sellers accept. Every phone Deviceli sells is at 80% or better.

Is 80% battery health bad?

No, but it is the line. Apple designs iPhone batteries to keep 80% after a set number of cycles, so a phone at 80% has reached normal end of design life. It still works; you’ll just get shorter days than when it was new.

How many charge cycles is too many for an iPhone?

Apple says iPhone 15 and later are designed to keep 80% capacity after about 1,000 complete cycles, and earlier models after about 500. Past those numbers, expect the health percentage to keep falling.

Does charging overnight damage the battery?

Not on a modern iPhone with Optimized Battery Charging on. It holds the charge at 80% and finishes charging shortly before you usually unplug.

Should I set my iPhone to stop charging at 80%?

If one charge comfortably gets you through the day, yes: it’s the gentlest setting. On iPhone 15 and later, it’s in Settings › Battery › Charging. If you need every bit of charge, leave it at 100% with Optimized Battery Charging on.

Can battery health go back up?

No. Capacity lost to aging doesn’t come back. The number can occasionally shift by a point after a software update recalibrates it, but the only way to restore it is a new battery.

Does low battery health lower my phone’s resale value?

Yes. At Deviceli, a battery below 80% counts as one issue, so the phone is priced as Damaged. It still gets a real offer.