How to Know If Your iPhone Battery Is Failing
Most iPhone batteries do not die suddenly. They fade, and by the time you notice you are carrying a charger everywhere. The trick is telling a worn battery from a software problem that clears itself in a few days — one costs money, the other does not.
Stop here if your screen is lifting at an edge, the phone rocks on a flat table, or the back has separated — the battery is swollen. Stop charging and using it, do not press or puncture it, and call 0466 446 461.
Do this now
Back the phone up to iCloud or a computer first. If the battery is swollen, do not charge it to back it up: bring it in and ask us to handle the data.
To get through today: turn on Low Power Mode (Settings > Battery), drop the brightness, and go easy on camera and navigation — the jobs that trigger shutdowns on a worn cell.
Which symptom do you have?
- Shuts down above 20 per cent? → Shutdowns
- Screen time halved? → Falling screen-on time
- Hot while idle, or charge figure jumping? → Heat and erratic charging
- Screen lifting or back separated? → Swelling
Shutdowns well above 0 per cent
A worn cell cannot hold its voltage under load: the phone reads 30 per cent, you open the camera, the voltage sags and iOS shuts down. Switching off at 20 or 30 per cent and reading healthier once plugged in is the most reliable symptom there is.
Screen-on time falling month after month
Settings > Battery shows screen-on time for the last 24 hours and 10 days. If a normal day gave five hours and now gives two and a half on the same habits, suspect the battery; an overnight change is usually software.
Heat and erratic charging
A degraded cell has higher internal resistance, so more energy becomes heat. Warm during navigation is normal; hot while idle in your pocket is not.
Charging that jumps from 40 to 60 per cent in a minute, or a figure that collapses the moment you unplug, means the reported charge no longer matches reality. Slow going over the last few per cent is not a fault — charging tapers deliberately near full, and Optimised Battery Charging pauses on purpose.
Swelling
A lifting screen, a phone that rocks on a flat table, or a separated back means the cell has swollen — a fire risk. Stop charging and using it, power it off, and keep it away from heat and anything flammable, not in a hot car.
Do not put it in household rubbish or kerbside recycling — swollen batteries need proper battery recycling. Call 0466 446 461 before bringing it to Unit 6/61 Market St, Wollongong, and we will tell you how to move it safely, or where to take it if you cannot get here.
Reading Battery Health properly
On current iOS the path is Settings > Battery > Battery Health (on iOS 16 and 17 the same screen is called Battery Health & Charging, and on those versions the charging options sit inside it rather than in their own Charging section).
Maximum Capacity is capacity as a percentage of new — an estimate, not a lab measurement, so watch the trend, not the daily number.
Service Recommended appears when capacity has degraded meaningfully. Apple's 80 per cent is a warranty threshold, not a cliff edge: a phone at 78 per cent can behave perfectly well, while one at 84 per cent can already shut down unexpectedly, because the real problem is voltage delivery, not raw capacity.
Peak Performance Capability is the line worth reading. It only appears once iOS has recorded an unexpected shutdown or applied performance management — if you do not see it at all, neither has happened, which is good news, not a missing feature.
If it says the battery is supporting normal peak performance, no battery-related performance management is active — though iOS can still slow the phone when it overheats or in Low Power Mode. Management, once applied, returns after every unexpected shutdown: a symptom, not a fix.
Before you pay: battery or software?
Did it start right after an iOS update? For a few days the phone re-indexes Spotlight, re-analyses photos and re-syncs iCloud, so drain is genuinely worse, then settles. Give it three or four days.
Is one app doing the damage? In Settings > Battery, switch to the last 10 days and tap Show Activity. If one app shows hours of background activity you never asked for, check its Background App Refresh and Location Services before replacing hardware.
Software drain concentrates in one or two apps; ageing is indiscriminate.
Optimised charging and charge limits
Sitting at 100 per cent, warm, for hours wears a battery fastest. Optimised Battery Charging holds the phone at 80 per cent overnight, finishing shortly before you wake. Leave it on.
iPhone 15 and later add a charge limit under Settings > Battery > Charging, holding the phone at 80 per cent, with 85, 90 and 95 per cent options on recent iOS versions. It still charges to 100 per cent occasionally, by design, to keep the gauge calibrated — not a fault.
Heat, cold and charge cycles
Apple's comfortable range is roughly 16–22°C ambient, and sustained exposure above 35°C can permanently reduce capacity. A car parked in the sun on a January afternoon in the Illawarra passes 60°C inside, and a phone left on the dashboard is being cooked — that damage does not come back.
Genuine cold — near freezing — temporarily reduces the runtime of any iPhone, and it recovers once warm. But in a coastal winter that rarely nears zero, a phone that shuts down in the morning cold is telling you the cell is already weak.
Batteries age by use, not birthdays. One charge cycle means using 100 per cent of capacity, not necessarily in one sitting. Apple has long rated iPhone batteries at about 80 per cent of original capacity after 500 cycles, and rates its newest models higher.
Replace the battery, or replace the phone?
If the screen, cameras and charging port are fine and the phone still gets iOS updates, a battery replacement is usually the smaller job, and can extend the useful life of a phone that is otherwise sound. Battery pricing is on our pricing page, and your quote is confirmed after inspection.
Lean towards a new phone if the device no longer gets security updates, or if the battery is one of several things failing. To check, open Settings > General > Software Update: if updates stopped coming a year or more ago and Apple no longer lists your model as supported, it is out of security support. Bring it in and we will tell you where your model stands; assessment is free either way.
What happens during a replacement
We never require or store your passcode; if a test needs the phone unlocked, we will ask you to unlock it.
The technician reads capacity and cycle count and load-tests the battery to work out whether it is actually the fault — sometimes it is not, and the assessment costs nothing either way.
The replacement itself is short: the old cell is released from its adhesive — pull tabs on older models, an electrically released bond on the newest — and a new one fitted, then the phone reassembled and tested under load. Ask any repairer what your model's teardown involves.
Ask about capacity too: request the cell's rated capacity in mAh and compare it with Apple's original figure for your model. Anything meaningfully below it gives less runtime whatever Battery Health reads, so ask us for the figure before you agree.
Water resistance is never the same after any repair: IP67 and IP68 ratings were tested on new devices in fresh water, never salt water or pool chemicals. Treat a repaired phone as splash-resistant at best. Most common models take about 45 minutes while you wait; some need a part ordered in, two to three days.
Battery replacements carry a 12-month warranty, on top of your rights under Australian Consumer Law.
The "Unknown Part" and battery messages
After a non-Apple battery replacement, iPhones commonly show an "Important Battery Message" saying the battery cannot be verified as genuine, or list it as an Unknown Part under Settings > General > About > Parts and Service History.
It means the new cell is not paired to the phone in Apple's system: an authentication notice, not a fault or a safety warning. Charging, performance and iOS updates are unaffected.
Pairing arrived with the iPhone XR and XS generation, so those and later models show the message; earlier ones do not. It can matter at resale, so tell us your model and we will confirm what yours will show.
Getting it checked
Bring the phone to Phone Repair Wollongong, Unit 6/61 Market St, Wollongong. Diagnostics are free, the quote is confirmed after inspection, and nothing proceeds without your approval. Call 0466 446 461, book online at phonerepairaustralia.com.au/book, prices on our pricing page, or track a repair at Track My Repair with your job number. Open seven days.