Your iPhone battery isn’t meant to last forever. Every lithium-ion battery has a finite number of charge cycles — Apple designs them to retain around 80% of their original capacity after 500 full cycles. If you’re a heavy user charging once or twice a day, you can hit that milestone in well under two years. The problem is that batteries don’t announce when they’re done. They just quietly start causing problems, and most people assume their phone is ageing out when the truth is that a single battery swap costing a fraction of a new handset would fix everything.
Here are the five signs that tell us — and should tell you — that it’s time for a new battery.
1. Your Battery Drains Faster Than It Used to
This is the most common complaint we hear. You used to get through the day comfortably. Now you’re reaching for the charger by early afternoon, or you’re carrying a power bank everywhere you go. The culprit almost always isn’t your apps or your settings — it’s a battery that’s lost a significant chunk of its capacity.
The good news is that Apple makes it easy to check. Head to Settings → Battery → Battery Health & Charging. You’ll see a percentage figure that tells you what proportion of the original capacity your battery still holds. If that number is below 80%, Apple itself considers the battery due for replacement. If you’re in the 70s or lower, the drain issues you’re experiencing make complete sense, and a new battery will feel like getting a new phone for a fraction of the price.
It’s also worth knowing that charge cycles accumulate even when you do partial charges. Topping up from 50% to 100% doesn’t count as a full cycle, but they add up over time. There’s no way to stop this — it’s just chemistry.
2. Your Phone Shuts Off With Battery Still Showing
This one is particularly frustrating. Your phone says 25% battery. Then it dies. You plug it in and it comes back on at 25% again. What’s happening?
When battery cells degrade, the voltage they can deliver becomes inconsistent. The percentage reading on your screen is calculated from voltage measurements, and when those measurements stop being reliable, the percentage stops being reliable too. Your phone’s processor detects that the battery can no longer supply enough power to keep the device running, and it shuts down — regardless of what the battery gauge says.
If your iPhone is dying at 10%, 20%, or even 30% battery remaining, that’s a strong signal that the cells inside have degraded significantly. This issue almost never improves on its own. The only fix is a replacement battery.
3. Your iPhone Is Running Noticeably Slower Than It Used to
This one surprises people, but it’s been well documented since Apple acknowledged it in 2017. Older iPhones with degraded batteries are subject to what Apple calls “performance management” — the system automatically limits the processor’s peak performance to prevent unexpected shutdowns caused by the battery being unable to deliver the power spikes the processor demands.
In plain language: your iPhone slows itself down on purpose to compensate for a weak battery. Apps take longer to open. Scrolling feels slightly sluggish. Everything just feels a bit less snappy than it once did.
Apple says this is to protect the user experience — and there’s logic to that — but it also means that a tired battery can make an otherwise perfectly capable phone feel like it needs replacing. It doesn’t. The battery does.
Checking Battery Health will usually confirm this. If performance management is active, iOS will tell you so on that same screen.
4. Your Battery Gets Hot During Normal Use
All phones generate some heat, and a warm phone during an intensive task like gaming or video streaming is perfectly normal. What isn’t normal is a phone that gets uncomfortably warm just from scrolling through Instagram, taking a phone call, or loading a webpage.
Excessive heat during light tasks is a sign that the battery is working harder than it should to deliver basic power. Chemical reactions inside a degraded cell are less efficient, and that inefficiency shows up as heat. This is both uncomfortable and damaging — sustained heat accelerates further battery degradation, which means the problem compounds itself over time.
If your iPhone is consistently warm to the touch during everyday use, get the battery checked. It’s worth doing sooner rather than later.
5. Your Phone Is Swelling or the Back Panel Is Bubbling
This is not just a battery problem — this is an emergency. If you notice that your phone’s screen has started to lift at the edges, the back glass has developed a bubble, or the phone no longer sits flat on a table, stop using it immediately.
Lithium-ion batteries sometimes enter a process called thermal runaway, where internal damage causes the cell to produce gas. This gas causes the battery to physically swell, and that swelling exerts enormous pressure on the phone’s components. In worst-case scenarios, swollen batteries can rupture and catch fire.
Do not continue using a phone with a swollen battery. Do not try to remove the battery yourself. Bring it to us — or any reputable repair shop — as soon as possible, and keep it away from flammable materials in the meantime. This one genuinely cannot wait.
How to Check Your Battery Health Right Now
It takes about 30 seconds. Open Settings, scroll down to Battery, and tap Battery Health & Charging. The percentage shown is your maximum capacity relative to when the phone was new. Here’s a rough guide to interpreting it:
100%–80%: Your battery is in healthy or acceptable condition. Some drain may be normal for an older phone.
Below 80%: Apple considers this the threshold for replacement, and you may already be noticing issues.
Below 75%: You’re almost certainly experiencing noticeable problems — drain, shutdowns, or sluggishness.
Below 70%: Replace the battery as soon as you can. The phone will feel genuinely rejuvenated afterwards.
Note that if your iPhone is very old and has been through a lot, the Battery Health screen may simply say “Service Recommended.” That means the battery health is degraded enough that iOS can’t even give you a reliable percentage — which is definitely time for a replacement.
What to Do Next
If any of the signs above sound familiar, the fix is simpler and cheaper than you might think. At GenioTech on Hilltown in Dundee, we replace iPhone batteries in most cases in under 30 minutes, and you don’t need an appointment — just drop in. We’re open Monday to Saturday, 9am to 5pm, and we’ll give you a straight answer about whether a battery replacement is the right solution before we do anything.
A new battery typically costs a fraction of what a new iPhone would, and in most cases it makes the phone feel brand new again. We’ve had customers come in convinced their phone was finished, only to leave 25 minutes later wondering why they waited so long.
If you’re not sure whether your symptoms point to the battery or something else, come in anyway. Diagnosis is free, and we’ll always tell you honestly what we find. You can also book or get in touch through our contact page if you’d like to check availability first.
Don’t replace your phone when you just need to replace your battery. Let us take a look.