- Shuts off with charge remaining = almost always a worn-out battery
- Shuts off when hot = overheating protection kicking in (battery-related)
- Shuts off then comes back on = software crash or failing battery
- Shuts off during calls or gaming = battery can’t handle load spikes
- A battery replacement fixes it in the vast majority of cases
The most common cause: a worn-out battery
A phone battery doesn’t just lose capacity as it ages — it also loses its ability to deliver power consistently. A degraded battery might show 30% charge but physically can’t supply the current a demanding task (a call, a game, the camera) needs in that moment. The phone detects a voltage drop it can’t recover from and shuts down to protect itself.
This is why random shutdowns are so common on phones that are 2–3 years old. The percentage shown on screen is an estimate — the real usable power in a worn cell is much less.
- iPhone: Settings → Battery → Battery Health & Charging. Below 80% = degraded. Below 75% = replace soon.
- Samsung: Dial *#0228# or Settings → Battery & Device Care → Diagnostics. Or download AccuBattery from the Play Store for a more detailed reading.
Other causes worth ruling out
Every phone has a thermal cutoff — it shuts down automatically if it gets too hot to prevent damage. If the phone feels warm before it cuts out, overheating is part of the problem. A degraded battery generates more heat under load, so the two issues often come together.
If the phone powers back on immediately after shutting off (rather than being unresponsive), it may be a software crash rather than a power failure. This is more common after major iOS or Android updates. Try updating to the latest version, or if it started after a recent update, check if others are reporting the same issue.
Even a phone that survived a water splash can have corrosion building up on internal components. Random shutdowns, charging problems, and flickering screens months after a water incident are all signs of delayed corrosion damage. This needs a professional clean — bring it in.
Is it software or hardware? Here’s how to tell
The simplest test: does it shut off while sitting idle doing nothing? If the screen is off, no apps are running, and it still shuts down — that’s almost certainly hardware (battery). Software crashes typically happen during active use.
On Android you can also try safe mode (hold the power button, then long-press “Power Off” until the safe mode option appears). Safe mode disables all third-party apps. If the random shutdowns stop in safe mode, a third-party app is causing the crash — uninstall recently added apps one by one.
If it shuts off in safe mode too, it’s hardware. The battery is the first thing to replace.
iPhone shutdowns and Low Power Mode
iPhones with degraded batteries are managed by Apple’s performance throttling system — iOS deliberately limits processor speed to prevent unexpected shutdowns. You might notice the phone feels slower than it used to, which is the system trying to compensate for the battery.
This is not a permanent fix — it’s a workaround that trades speed for stability. It will get worse as the battery degrades further. A new battery removes the throttle entirely and restores full performance.
A phone that shuts down unexpectedly mid-call, mid-navigation, or while you’re out and about is more than an inconvenience. In an emergency, you need your phone to work. And as the battery continues to degrade, the shutdowns get more frequent. A battery replacement is the fix — straightforward, same-day, and it makes the phone feel new again.
Phone shutting down? Walk in — we’ll check it in minutes.
Battery replacements done same day. We’ll run a health check first and tell you exactly what’s happening before anything is touched. Clapham Junction, open 7 days.