Battery capacity loss: when is it wear and when is it a defect?

Battery complaints are the most common warranty claim that gets refused, and usually correctly. Lithium-ion cells lose capacity with every charge cycle. That is chemistry, not a fault, and no warranty covers it.

But there is a threshold, and manufacturers publish one. Knowing where it sits turns a vague complaint into a specific claim.

The threshold

Most manufacturers state that a battery should retain a defined percentage of its original capacity after a stated number of charge cycles, or within the warranty period. Falling below that is a defect. Staying above it is wear.

The exact figures differ by brand and by product, so look up your model’s stated figure rather than relying on a general number. It is usually in the warranty documentation or the battery service page.

How to read your actual numbers

iPhone: Settings, Battery, Battery Health & Charging. Shows maximum capacity as a percentage.

Android: varies. Some manufacturers expose it in a diagnostics menu or their own service app. Otherwise a battery information app can read the reported design capacity and current capacity.

Windows laptops: open a command prompt and run powercfg /batteryreport. It generates an HTML file showing design capacity, full charge capacity and cycle count. This is built in and most people do not know it exists.

Mac: hold Option, click the Apple menu, System Information, Power. Shows cycle count and condition.

Screenshot whatever you find. A report generated by the manufacturer’s own software is the strongest evidence you can bring.

Symptoms that are defects, not wear

Some battery problems are not about capacity at all, and these are much easier claims:

• The battery will not charge, or charges only intermittently
• The device shuts down at a percentage well above zero
• The battery drains from full to empty in a very short time with no load
• The reported capacity drops sharply rather than gradually
• Physical swelling

Why claims get refused

Above the threshold. If your battery is at 85 percent and the threshold is 80, the claim fails. This is the most common outcome and it is correct.

High cycle count. Wear scales with cycles. A battery with a very high cycle count that has degraded proportionately is behaving as designed.

Third-party charger blamed. Note the limit here. Under the Magnuson-Moss Warranty Act, using a third-party charger cannot on its own void a warranty. The manufacturer would have to show that the charger caused the failure. A certified third-party charger operating within specification did not cause a cell to swell.

Practical steps that extend battery life

Worth knowing because they cost nothing and the effect is real.

Heat is the main enemy. A device charging inside a case in direct sun ages faster than one that stays cool. Avoid leaving devices in cars.

Avoid habitually running to zero and sitting at 100 percent for long periods. Where a device offers optimised or limited charging, turn it on — particularly on a laptop that lives permanently on a charger.

None of this prevents degradation. It slows it, which over a few years is the difference between replacing a battery and replacing a device.

If the battery genuinely needs replacing out of warranty

Manufacturer battery replacement is usually reasonably priced relative to the device, and it is one of the highest-value repairs available. A device with a fresh battery and remaining software support is often good for years more.

Compare the manufacturer price against an independent shop and, if you are comfortable with it, a DIY replacement. On many devices this is one of the more approachable self-repairs. On devices with heavy adhesive it is not.