At What Battery Health Should You Replace an iPhone Battery?

Where to find the number

On an iPhone, open Settings › Battery › Battery Health & Charging. The figure at the top is Maximum Capacity, shown as a percentage. Recent iPhones also list a cycle count, manufacture date and date of first use under Settings › General › About, which is useful if you bought the phone used and want to know what you actually got.

What Maximum Capacity actually means

It’s an estimate of how much charge the battery can hold now compared with when it was new. At 100% it stores what it was designed to store; at 85% it stores roughly 85% as much, which in practice means a shorter day rather than a broken phone.

Two things worth knowing. First, it’s an estimate, calculated by the phone from how the battery behaves during charge and discharge — it isn’t a lab measurement, and it can sit still for weeks and then step down two points at once. Second, it says nothing about the battery’s ability to deliver power quickly, which is a separate property and often the one that fails first.

The 80% line, and where it comes from

Apple rates iPhone batteries to retain up to 80% of original capacity through a set number of complete charge cycles under normal conditions — 500 cycles on older models, and 1,000 cycles on iPhone 15 and newer. A cycle means using 100% of the battery’s capacity in total, not plugging in once: two days of using half the battery each day counts as one cycle.

So 80% isn’t a cliff the battery falls off. It’s the point at which the battery has done the job it was designed and warranted to do, and where Apple considers it consumed. That’s why it makes a sensible replacement threshold for most people.

“Service Recommended” and the peak performance message

Once Maximum Capacity drops meaningfully below 80%, the Battery Health screen replaces the reassuring text with a service message telling you the battery’s health is significantly degraded and that replacing it will restore full performance and capacity. Nothing is disabled and nothing is unsafe — it’s a recommendation.

The message that deserves more attention is the other one. If your iPhone has shut down unexpectedly because the battery couldn’t deliver the peak power the processor demanded, iOS applies performance management to prevent it happening again, and says so on the same screen. You can switch that management off, but it re-applies after the next unexpected shutdown. Either way, that message means the battery is already struggling under load, and it’s worth acting on regardless of what Maximum Capacity says.

Is 85% battery health good?

Yes, generally. At 85% you’re within normal wear, the phone should behave normally, and you’ll notice it mainly as less runway at the end of a heavy day. It isn’t a reason to replace anything on its own. If a phone at 85% is dying by mid-afternoon, the battery isn’t the whole story — check Settings › Battery for an app burning through power in the background, and check whether the phone is running hot, which drains and degrades at the same time.

Symptoms that matter more than the percentage

• Shutdowns at a high percentage. The phone dies at 30% or 40% and then, back inside, restarts showing 25%. That’s a battery that can’t hold voltage under load.
• Sudden drops. 60% to 12% in one step, or a percentage that jumps back up after charging briefly.
• Dying in the cold. Montréal winters are hard on weak batteries. Lithium cells give less usable power in the cold, and a worn one shows it first — that’s often the earliest real symptom.
• Only working plugged in. A phone that shuts off the moment it leaves the charger has effectively no usable battery left.
• Heat during normal use, especially while charging.

What actually wears a battery out

Heat, above everything else. Charging in a car in July, gaming while plugged in under a thick case, leaving the phone on a dashboard or a windowsill — heat does more damage than any charging habit. Apple specifies an ambient operating range of roughly 0°C to 35°C for a reason.

After heat: sitting at 100% for long stretches at high temperature, and repeatedly running down to 0% and leaving it there. Cycles themselves matter too, but you can’t avoid using your phone, and modern fast charging is far less of a villain than the internet believes — the heat it can produce is the part worth managing. If you’re storing a device for months, leave it around half charged rather than full or empty.

Optimised charging and the 80% limit

Optimised Battery Charging learns your routine and holds the phone at 80% overnight, finishing the charge just before you normally wake up, which cuts the hours spent sitting at full. Leave it on. iPhone 15 and later also offer a hard charging limit — 80%, with intermediate steps on newer iOS versions — which is worth using if you’re usually near a charger and don’t need the last stretch of battery. Neither feature repairs an old battery; both slow down the wear on a healthy one.

Checking battery health on Samsung and Android

Android doesn’t present this as uniformly as iOS. Many Galaxy phones report battery status as a condition — good or normal — in the device care diagnostics or in the Samsung Members app, rather than as a percentage, while newer models and newer Android versions do surface a health figure. The symptoms are identical regardless of the brand: shutdowns above 20%, sudden drops, heat, and swelling. If the numbers on your Galaxy or other Android phone aren’t telling you much, the behaviour will.

What a replacement involves, and what to do first

Back up before any repair — iCloud or a computer, either is fine — and make sure you know your Apple ID password and passcode. A battery replacement doesn’t erase anything, but backing up first is basic insurance and takes the stress out of the whole thing.

The job itself means opening the phone, releasing the display, disconnecting the battery, removing adhesive that Apple has redesigned several times across models, fitting and seating the new cell, and resealing the device so its water resistance is properly restored. One thing to know going in: iPhones record parts history, and depending on the model and the battery fitted, iOS may display a message saying it can’t verify the battery is genuine, and the Maximum Capacity readout can become unavailable. That’s a software verification behaviour, not a statement about how the battery performs — ask us what applies to your exact model before we start.

Sub Tech Repairs handles batteries for iPhones, phones of every brand, iPads and MacBooks — laptops report cycle count and a battery condition of their own, and the wear story there is exactly the same. We’re walk-in seven days a week at 757 Rue Beaubien Est beside Beaubien metro, with 5,500+ Google reviews and a 4.9 rating. Every repair is covered by a 1-year warranty.