Batteries
How an old battery slows your phone down
Almost every week someone hands us a two or three-year-old phone and says the same thing: "it's just getting old, everything takes forever now." Nine times out of ten the processor is exactly as fast as the day they bought it. The battery isn't, and that's what they're feeling.
What actually happens inside an ageing battery
A phone battery is a lithium-ion cell, and it wears in two ways at once. It loses capacity (how much charge it can hold, which is the number you see as "battery health"), and it gains internal resistance (how hard it is to pull current out of it quickly). The first one shortens your day. The second one is what makes your phone slow.
When you tap an app icon, the processor jumps from near-idle to full speed in a few milliseconds and demands a large gulp of current. A healthy cell delivers it without flinching. A worn cell can't: its voltage sags under the sudden load, and if it sags far enough the phone browns out and switches off — the infamous shutdown at 30% on a cold morning.
Why your phone chooses to slow down
Faced with a battery that can't deliver peak current, a phone has two options: crash, or ask for less. Modern phones ask for less. They cap the processor's peak speed, stretch out how quickly it ramps up, and dim or throttle other power-hungry parts, all to keep the demand inside what the battery can actually supply.
Apple made this explicit after the 2017 controversy: iPhones with a degraded battery apply "performance management", and you can see it stated in Settings → Battery → Battery Health & Charging. Android phones handle it less visibly, but the physics is identical, and so is the result — apps take longer to open, the camera hesitates before it fires, scrolling stutters, and games drop frames.
The important part: this isn't your phone being deliberately crippled to sell you a new one. It's the phone protecting itself from a component that's worn out, and that component is replaceable.
How to tell it's the battery and not the software
These point at the battery:
- The phone is noticeably faster right after you charge it, and gets sluggish as the day goes on.
- It shuts down suddenly with charge still showing, especially in the cold.
- Heavy jobs — camera, video calls, games, navigation — are where it struggles most.
- Battery health is under about 80%, or the phone is past 500 charge cycles.
- A factory reset made no difference (people usually try this first, and it rarely helps).
These point at something else: the phone is slow even at 100%, storage is nearly full, it's hot to the touch when idle, or the slowdown started the day you installed a major update.
Checking your battery in 30 seconds
On an iPhone, go to Settings → Battery → Battery Health & Charging and look at Maximum Capacity. Below 80%, Apple itself flags the battery as degraded. On recent Android versions, Settings → Battery → Battery health (or Battery information) shows capacity and cycle count on many models; where it doesn't, we can measure it on the bench in a couple of minutes.
One caveat worth knowing: a battery can be failing under load while still reporting a respectable health percentage. If the phone shuts down early or stutters under heavy use, trust the behaviour over the number.
What actually changes after a replacement
With a fresh cell, the reason for the throttling is gone, so the phone stops holding back. Customers describe it as "like a new phone", which is not marketing: it's a three-year-old processor finally being allowed to run at the speed it always could. You also get your full screen-on time back, and the random shutdowns stop.
A battery replacement at Five Star Repairs starts from $59, is usually done same-day and often within the hour, and carries our 12-month workmanship warranty. Against the price of a new phone, it's the cheapest performance upgrade there is.
Book a battery replacement Battery replacement prices