How to test a laptop or phone battery — charge, drain, and health

Laptop and phone batteries only

Plenty of people searching for how to test a battery are holding a car battery or a handful of AA cells and a multimeter. This page isn’t about either of those. It covers the rechargeable pack built into a laptop, Chromebook, tablet, or phone, and specifically two things: how to watch charge and discharge behaviour, and where each operating system exposes real health figures.

If you need a load test on a 12 V car battery or a continuity check on a loose cell, you want a different guide and different equipment. Nothing below applies.

What a browser can and can’t see

On Chromium browsers, meaning Chrome, Edge, and the various things built on them, the Battery Status API can report three things: the charge percentage, whether the device is charging or running on battery, and rough time-to-full or time-to-empty estimates. That’s genuinely useful when you want to confirm the charge reading is moving as you plug and unplug, without installing anything.

What it cannot report is cycle count, design capacity, full charge capacity, or a manufacturer health percentage. Browsers deliberately withhold those, because they’d make it far too easy to fingerprint and track individual devices. Safari never implemented the API at all, and Firefox removed it years ago, so a “not supported” message on those browsers is expected rather than a sign of anything wrong.

Time estimates are worth treating carefully. They swing wildly with CPU load and screen brightness, so read them as a direction of travel rather than a specification. A laptop that’s draining fast needs the usage breakdown and a capacity report, not a single number from a browser.

In practice this splits into a two-step habit. Use the browser or your system tray icon to watch live charge behaviour, and use the tools in the next few sections when you want to know about wear. Confusing the two is why people conclude a battery page has failed when it never claimed to measure health in the first place.

Checking battery health on Windows

Windows has a proper built-in report, and it’s the honest answer for wear on a Windows laptop.

Open Command Prompt, PowerShell, or Windows Terminal and run powercfg /batteryreport. Windows generates an HTML file and prints the path where it saved it, which by default is whatever folder your terminal was sitting in. That’s often your user profile folder if you launched it from the Start menu. If you’d rather choose the location yourself, run powercfg /batteryreport /output "C:\Users\YourName\Desktop\battery-report.html" instead.

Open the resulting file in any browser. The number you want is near the top: compare Design Capacity, which is what the pack held when it left the factory, against Full Charge Capacity, which is what it holds today. A large gap between them is the straightforward hardware explanation for why your laptop doesn’t last as long as it used to.

The same report includes a usage history over recent weeks, which is genuinely helpful for separating a battery that’s worn out from a battery that got hammered by one badly behaved application yesterday.

The Power & battery screen in Settings is still worth a look for per-app drain, but for capacity itself, the report is what you want.

MacBook battery health and cycle count

For a quick answer, open System Settings, go to Battery, and open Battery Health. That gives you the condition summary and whatever charge management options macOS offers for your model.

For cycle count and the full detail, you need System Information. Hold Option, click the Apple menu, and choose System Information, or reach it through System Report from the About This Mac screen. In the sidebar under Hardware, select Power. Cycle count and condition are both listed in the battery information section.

A condition of “Service Recommended”, or a cycle count close to Apple’s published limit for your model, means you should plan on a replacement pack. No software tweak restores lost capacity. On the other hand, a MacBook that drains quickly while reporting a healthy condition and a low cycle count is usually being drained by screen brightness, a runaway process, or a peripheral pulling power over USB.

Phone battery health check

On an iPhone or iPad, open Settings, Battery, then Battery Health & Charging. The wording shifts slightly between iOS versions, but Maximum Capacity is the wear figure most people are after. Charging optimisation settings and any peak performance notice live on the same screen.

Android is messier. Settings, Battery, along with any manufacturer-specific battery care or device care screen, will show you what’s been using charge. Many Android builds simply don’t expose a wear percentage to users. Some manufacturer support apps add one, and there are hidden menus and ADB commands floating around, but those are easy to misread and vary enormously between brands. If you need a number you can rely on, use whatever route your manufacturer officially documents.

A phone that loses a large chunk of charge overnight while doing nothing usually needs either a look at which apps are waking it up, or a new battery if it’s done enough cycles.

Fast drain versus genuine wear

A laptop battery draining fast has two quite different explanations, and they need different responses.

The first is that something is drawing power right now. A bright display, background sync, a weak Wi-Fi signal making the radio work harder, or an application stuck in a loop. Your operating system’s battery usage list will name the culprit, and this costs nothing to fix.

The second is that the pack itself has worn out. Full Charge Capacity sitting well below Design Capacity in the Windows report, or Maximum Capacity well below 100% on iOS and macOS, with runtime collapsing even when the machine is idle.

Deal with the first before you spend money on the second, and confirm the second with the built-in tools rather than a third-party app offering a “battery score”.

There’s a useful way to tell them apart. If runtime is only short when one particular app is open, that app is the story. If runtime is short at idle, after a reboot, with brightness at a moderate level, open the capacity report.

A few things fall outside both categories and need attention regardless of what the health percentage says. A pack that has visibly swollen, enough to bow the case or lift the trackpad, should be dealt with promptly and not charged in the meantime. Sudden shutdowns at 30% or 40% suggest the pack can no longer deliver current under load even if its capacity reads acceptably. And “plugged in, not charging” with a charger you know is good is a charging circuit problem rather than a battery health one.

While we’re clearing things up: the old advice about fully discharging a battery periodically to recalibrate it belongs to an earlier generation of cells. Modern lithium-ion packs don’t benefit, and deep discharges are mildly harmful. Follow your manufacturer’s current guidance instead. Do keep firmware and BIOS updates current if your manufacturer has published anything about charging behaviour or unexpected shutdowns, since those are fixed in firmware rather than anywhere you can see.

Watching charge behaviour live

When all you want is to confirm that the charge percentage and charging state update correctly as you plug in and unplug, and you’re on a Chromium browser that still exposes the API, open a live charge-level reading and compare it against your menu bar or system tray. It runs in your browser and nothing is uploaded.

For wear, cycle count, and design capacity, stick with powercfg /batteryreport on Windows, the Power section of System Information on a Mac, or the Battery Health screen on your phone. Those values simply aren’t visible to a web page.