iPhone Battery Health: What Percentage Is Too Low? (2026 Guide)
Every lithium-ion battery wears out, and your iPhone keeps a running score of how worn yours is. That score lives in Settings under Battery Health & Charging, shown as a single "Maximum Capacity" percentage. It is the number people search for the moment their phone starts dying by mid-afternoon – and the question is almost always the same: what percentage is too low?
This guide gives you a straight answer, explains what the percentage measures, and explains why the number alone does not tell the whole story – some of the worst batteries we see on the bench still read in the 80s.
Direct answer: An iPhone battery is generally considered worn once Maximum Capacity drops below 80% – that is the point Apple flags the battery for "Service" and where performance management can begin. Many people cope fine into the low 80s, but once you are in the 70s or lower a replacement is usually the right call. Crucially, percentage is not the only signal: sudden shutdowns, rapid drain, slow performance or any swelling mean replace now, whatever the number says. A celltech iPhone battery replacement starts from £39.95, carries our 27-month guarantee, and is done by tracked, insured UK-wide mail-in.
How to check your iPhone battery health
You do not need an app or any special tool. Apple builds the figure straight into iOS:
- Open Settings
- Tap Battery
- Tap Battery Health & Charging
You will see Maximum Capacity (a percentage) and Peak Performance Capability (a short status message). On iPhone 15 and later, Apple also shows a cycle count and the date the phone was first used – handy for checking whether a second-hand handset is as young as the seller claimed.
If the menu is greyed out, it usually means a previous repairer fitted a non-genuine cell without recalibrating it, so iOS hides the reading and shows an "Unknown Part" notice instead – worth knowing before you buy a used iPhone.
What "Maximum Capacity" actually means
Maximum Capacity is a measure of your battery's current capacity relative to when it was new. A brand-new iPhone reads 100%. If it shows 85%, the battery now holds roughly 85% of the charge it could hold on day one – so you get about 85% of the original screen time between charges.
It is a relative figure, not an absolute one: a bigger phone at 85% may still outlast a smaller phone at 95%. The percentage tells you how much your own battery has degraded, which is exactly what you want when deciding whether to replace it.
Degradation is driven mainly by charge cycles (one cycle equals a full 0–100% worth of charge) and by heat. Apple designs iPhone batteries to retain up to 80% of capacity at 500 cycles on older models, and at 1,000 cycles on iPhone 15 and newer – roughly two to three years of typical use before most people notice the difference.
Battery health percentages: what is good, what is not
Here is how to read the number in plain terms, based on what we see come through the workshop:
- 100–90% – excellent. This is healthy. Nothing to do. A drop from 100% to the mid-90s in the first year is completely normal and not a fault.
- 90–80% – normal ageing. The phone is doing exactly what it is meant to. You may notice slightly shorter screen time, but it is gradual. No action needed unless you are also seeing the warning signs below.
- Around 80% – the watershed. At 80% Apple stops calling the battery healthy. You may see a "Service" recommendation, and the system can start applying performance management to prevent shutdowns. Many people still get through a day; many others decide this is the moment to replace.
- 80–70% – you will feel it. Below 80% the daily drop-off becomes obvious: shorter runtime, faster fall under load (camera, gaming, navigation), and a phone that needs a top-up to reach the evening. A replacement starts to make clear sense here.
- Below 70% – replace. At this point the battery is well past its service life. Expect significant runtime loss and a higher chance of sudden shutdowns. There is no benefit to holding on.
These are guidelines, not hard rules: a battery at 82% that shuts the phone off in the cold is worse, in practice, than a stable one at 78%. Use the percentage as a starting point, then weigh it against how the phone actually behaves.
Is 70% battery health too low? (and the iPhone 11 question)
This is the single most common version of the question we get, often phrased as "70 battery health on my iPhone 11 – is that bad?" The honest answer: yes, 70% is low, and on a phone of the iPhone 11's age it is a sensible point to replace the battery.
An iPhone 11 launched in 2019, so by now most are several years and many hundreds of cycles into their life. At 70% the battery holds around 30% less charge than when new – the difference between comfortably reaching bedtime and reaching for a charger at lunch. The phone itself is still perfectly capable, so replacing a worn battery is the cheapest way to make it feel new again and far better value than upgrading the whole handset.
The same logic applies to any model sitting in the low 70s. If everything else about the phone is healthy, a battery is the highest-impact, lowest-cost repair you can do. At celltech, an iPhone 11 battery replacement is £44.95 (with a higher-capacity premium cell available at £54.95), and it carries our 27-month guarantee. For the full economics of the decision, see is it worth replacing an iPhone battery?
"Peak Performance Capability" and shutdown messages
Underneath Maximum Capacity sits a second line: Peak Performance Capability. On a healthy phone it reads something like "Your battery is currently supporting normal peak performance." That is the message you want.
If you instead see a notice that your iPhone "experienced an unexpected shutdown because the battery was unable to deliver the necessary peak power," iOS has switched on performance management. To stop the phone abruptly powering off, it dynamically eases back processor speed at moments of high demand. You might notice apps opening more slowly, the keyboard lagging, or frame-rate dips in games. This is the famous "throttling" – and it is a symptom of a worn battery, not a fault with the chip.
You can switch performance management off after a shutdown event, but that just trades smoothness for the risk of sudden shutdowns. The real fix is a new battery: once a fresh cell can deliver full peak power again, performance management is no longer needed and the phone returns to full speed. A "Service" message means much the same thing – the battery has degraded (typically below 80%) and Apple is recommending replacement. It is informational, not an error, and the phone is safe to use in the meantime.
Battery health is not the only signal
If you take one thing from this guide, take this: the percentage can lie by omission. A battery can read in the 80s and still be the right one to replace. These signals matter more than the number:
- Unexpected shutdowns. A phone that powers off at 30%, 40% or in the cold has a battery that can no longer hold voltage under load. Replace it – this is the clearest warning of all.
- Fast or erratic drain. Dropping 20% in minutes, or jumping from 40% straight to dead, points to a failing cell rather than a software issue. If you are chasing battery drain, our guide on why your iPhone battery drains so fast walks through the software checks first.
- Swelling. A screen lifting at one edge, a back that no longer sits flat, or a wobble on the table is a swelling battery. Stop charging it and get it replaced promptly – a swollen cell can damage the screen and is a genuine safety risk.
- Overheating. A phone that runs hot during ordinary tasks or while charging may have a stressed battery.
- It will not hold a charge or charges very slowly. Sometimes a charging-port fault rather than the battery – which is exactly why our diagnostics check both.
Any one of these means replace, regardless of whether Maximum Capacity reads 95% or 75%. Swelling in particular is not a "wait and see" situation.
How to slow battery degradation
You cannot stop a battery ageing, but you can slow it down and squeeze more good years out of it:
- Leave Optimised Battery Charging on. This iOS feature (in the same Battery Health menu) learns your routine and holds the charge at 80% overnight, finishing to 100% just before you wake. Less time sitting at a full charge means slower wear.
- Avoid the extremes. Lithium-ion batteries are happiest in the middle. Try not to leave the phone at 100% for hours or routinely run it flat to 0%. Topping up little and often is gentler than deep cycles.
- Keep it cool. Heat is the biggest accelerant of degradation. Don't leave the phone on a car dashboard, charging under a pillow, or in direct summer sun. If it gets hot while gaming or navigating, take the case off.
- Use sensible chargers. Good-quality cables and adapters matter; very cheap, uncertified chargers can run hot and stress the cell.
- Update iOS. Apple periodically improves charging and power management in software updates. On newer models you can also cap charging at 80% permanently if longevity matters more to you than maximum screen time.
When to replace – and what it costs
Put simply, replace the battery when either of these is true:
- Maximum Capacity is in the 70s or below, or
- You are seeing real-world symptoms – shutdowns, swelling, fast drain, throttling – at any percentage.
A battery is the most cost-effective repair an iPhone ever needs: for a fraction of the price of a new handset you reset the component that ages fastest and get the original screen time back. We fit cells honestly tiered by quality – a standard high-grade cell, and a premium higher-capacity option on many models. Whichever you choose, every standard battery replacement carries our 27-month guarantee – more than double the 12 months most independent UK repairers offer, and far longer than Apple's 90-day repair warranty. Pricing is published openly below rather than hidden behind a quote form, and the whole job is done by tracked, insured UK-wide mail-in, posted back to you fixed.
iPhone battery replacement cost
These are celltech's current published prices for a standard battery replacement. Diagnostics are free on standard repairs like this, and your data is never touched during a battery swap.
| iPhone model | Battery replacement (from) |
|---|---|
| iPhone SE (2020) | £39.95 |
| iPhone SE (2022) | £44.95 |
| iPhone 11 | £44.95 |
| iPhone 11 Pro | £44.95 |
| iPhone 11 Pro Max | £59.95 |
| iPhone XR / XS / X | £54.95 |
| iPhone 12 | £44.95 |
| iPhone 12 Pro | £49.95 |
| iPhone 12 Pro Max | £54.95 |
| iPhone 13 | £44.95 |
| iPhone 13 Pro / Pro Max | £74.95 |
| iPhone 14 | £69.95 |
| iPhone 14 Pro | £84.95 |
| iPhone 15 | £74.95 |
| iPhone 16 | £54.95 |
A higher-capacity premium cell is available on most models for a little more – for example, £54.95 on the iPhone 11 or £69.95 on the iPhone 13. For the full model-by-model breakdown and how we compare with Apple and the high street, see our iPhone battery replacement cost guide. For reference, Apple's published out-of-warranty battery service in the UK runs to roughly £65–£105 depending on model (subject to change), typically with a 90-day warranty.
Frequently asked questions
What iPhone battery health percentage is too low?
Below 80% is where Apple flags the battery for "Service" and performance management can begin, so 80% is the watershed. In practice, once you are in the 70s or lower a replacement is the sensible choice, because runtime loss becomes obvious and the risk of shutdowns rises. That said, replace at any percentage if you see shutdowns, swelling or rapid drain.
Is 80% battery health bad?
Not bad, but it is the turning point. At exactly 80% the battery has reached the end of the capacity Apple guarantees, and you may see a "Service" note. Plenty of people use a phone happily at 80% for a while longer. If the daily runtime still suits you and there are no warning signs, you can wait; if you are constantly topping up, replace it.
Will replacing the battery reset my battery health to 100%?
Yes. Fitting a new battery restores Maximum Capacity to 100% (it may read very slightly under for the first few cycles until iOS calibrates), brings back the original screen time, and switches off performance management so the phone runs at full speed again.
Is my data safe during a battery replacement?
Yes. A battery swap does not touch your storage, so your photos, messages, apps and settings remain exactly as they were. The phone boots back up as you left it. We still recommend keeping a routine backup, as everyone should, but no data is altered during the repair.
Should I replace the battery myself?
We would advise against it. Modern iPhones use strong adhesive and a sealed assembly, the battery is a fire risk if punctured or bent during removal, and fitting a non-genuine cell without proper recalibration causes iOS to hide the battery health reading and show warning messages. A professional replacement avoids all of that and keeps the data and the diagnostics intact.
How long does a new iPhone battery last?
Expect a similar lifespan to the original – broadly two to three years of typical use before it drifts down towards 80% again, depending on how hot you run the phone and how many cycles you put through it. Our 27-month guarantee on standard battery replacements is set to cover that real-world service life.