Open Settings, Battery, Battery Health & Charging, and you get a single percentage. People treat it like a fuel gauge and panic when it drops below 90. It is not a fuel gauge, and 89% is nothing to worry about.
Here is what the number means and when it actually matters.
What the percentage measures
Maximum Capacity compares what your battery can hold today against what it could hold when it was new. At 85%, a full charge holds roughly 85% of the energy it originally did — so if the phone used to last fifteen hours of your normal usage, it now lasts around thirteen.
Crucially, this is about runtime, not about the phone being broken. A phone at 85% is a completely healthy phone that needs charging a bit sooner.
Why every battery declines
Lithium-ion cells wear out chemically through use. Every full charge cycle — 100% of capacity used, whether in one go or across several days — causes a tiny amount of irreversible change. Heat accelerates it sharply. Nothing you do will prevent this entirely; the goal is only to slow it down.
A typical iPhone loses somewhere around 10–20% of capacity in its first two years of normal use. That is expected behaviour, not a defect.
The 80% line
Eighty percent is the number everyone quotes, and there is a reason. Apple designs batteries to retain up to 80% capacity over a stated number of cycles, and it is roughly the point where two things start happening together:
- The runtime drop becomes something you notice in daily use rather than something you only see in a settings screen.
- The battery becomes more likely to struggle under load — cold weather, camera use, gaming — which is where unexpected shutdowns come from.
This is why our Battery Life Guarantee sets 80% as the minimum on every device we sell. Nothing goes out the door below it.
The signs that matter more than the number
Replace the battery when you see these, whatever the percentage says:
- Sudden shutdowns — the phone dies at 25% or 30%. The clearest signal there is.
- Rapid drops — falling from 60% to 30% in a few minutes of light use.
- "Peak Performance Capability" warning — iOS is telling you it has started throttling the processor to prevent shutdowns. Your phone is now slower because of the battery.
- Heat during ordinary use — warm during gaming is normal; warm while reading messages is not.
- Any physical swelling — a screen lifting at the edge or a bulging back. Stop using the phone and bring it in immediately. Do not press on it and do not charge it.
What a replacement gets you
A new battery restores full runtime and removes any performance throttling, which is why an older iPhone often feels noticeably faster after a battery replacement. On a device that is otherwise working well, it is the cheapest meaningful upgrade available — typically a fraction of what a replacement phone costs.
Buying refurbished from us? You can have a brand-new battery fitted by our technicians before the phone is dispatched for $53. It adds one business day to dispatch and means you start at full capacity rather than at the 80% floor.
Habits that genuinely slow the decline
Most battery advice online is folklore. These four are not:
Keep it cool
Heat is the biggest single accelerator of battery ageing. Do not leave the phone on a car dashboard, do not charge it under a pillow, and take it out of a thick case if it gets hot while fast-charging.
Avoid living at 0% and 100%
Batteries age fastest at the extremes. Staying roughly between 20% and 80% is easier on the cell than draining flat and topping to full every day. Leave Optimised Battery Charging on — it learns your routine and holds at 80% until shortly before you normally wake up.
Use decent chargers
Cheap unbranded chargers can deliver unstable power. Stick to reputable gear.
Stop chasing cycle counts
You do not need to fully discharge the phone periodically. That advice belongs to nickel-based batteries from decades ago and does nothing but add wear to a lithium-ion cell.
Checking it yourself
On iPhone: Settings → Battery → Battery Health & Charging. On most Samsung devices: Settings → Battery and device care → Diagnostics, or via the Samsung Members app.
When to get it looked at
If your health reading is below 80%, if you are getting shutdowns, or if there is any swelling at all, book a diagnostic or a battery replacement with us. We handle iPhone, Samsung, Pixel and iPad batteries in-house at Shop 7A, 118 Church Street, Parramatta, and the work is covered by warranty.
If the phone has other problems alongside the battery, it may be worth comparing the repair against a refurbished replacement with a fresh 12-month warranty — we will give you an honest view either way.
