The fastest way to check your battery

The quickest check is to look at your device's battery percentage right now. On most phones and laptops, this number appears in the top corner of your screen — on iPhones in the upper right, on Android phones in the upper right, on Windows laptops in the lower right taskbar, on Macs in the upper right menu bar. If that number is below 20 percent, your battery is low and you should charge soon. If it is below 5 percent, charge immediately or your device will shut down without warning.

But a percentage alone does not tell you whether your battery is actually failing. A battery that drops from 100 to 0 percent in two hours when it used to last all day is dying, even if it shows 50 percent right now. A battery that will not hold a charge at all, or that swells visibly, is failing and needs replacement. The steps below show you how to dig deeper and find out which situation you are in.

Key Takeaways

  • Check your battery percentage in the top or bottom corner of your screen — below 20 percent means charge soon, below 5 percent means charge now.
  • On Windows, open Settings and search for "battery report" to see how much capacity your battery has lost over time.
  • On Mac, hold Option and click the battery icon in the menu bar to see the battery's current condition listed as "Normal" or "Replace Now".
  • On iPhone, go to Settings > Battery > Battery Health to see the maximum capacity your battery can hold compared to when it was new.
  • A swollen, cracked, or leaking battery is a safety hazard and should not be used — take the device to a repair shop or manufacturer immediately.

Check battery health on Windows

Windows keeps a detailed record of your battery's condition. Open the Start menu and type "battery report" into the search box. Click "Create a battery report" when it appears. Windows will open a folder with an HTML file named something like "battery-report-2024-01-15.html" — double-click it to open it in your web browser.

Look for the section called "Battery Information" near the top. Find the line that says "Design Capacity" — this is what your battery could hold when it was brand new. Below that, find "Full Charge Capacity" — this is what it can hold right now. Divide the full charge capacity by the design capacity and multiply by 100. If the result is 80 percent or higher, your battery is still healthy. If it is between 50 and 80 percent, your battery is aging but still usable. If it is below 50 percent, your battery is failing and you should plan to replace it soon.

The report also shows you "Recent Usage" — a table of how long your device ran on battery power each time you unplugged it. If those numbers are dropping sharply over the past week or two, your battery is degrading faster than normal.

Check battery health on Mac

Hold down the Option key on your keyboard and click the battery icon in the menu bar at the top right of your screen. A small menu will appear showing your current battery percentage and a line that says "Condition:" followed by either "Normal", "Replace Soon", "Replace Now", or "Service Battery". If it says "Normal", your battery is fine. If it says "Replace Soon" or "Replace Now", your battery is failing and you should have it serviced within the next few weeks or days.

If you want more detail, open System Settings, click "General" in the left sidebar, then click "About". Scroll down to find "System Report" and click it. In the window that opens, click "Power" in the left sidebar. Look for the line that says "Health Information" — it will show you the current maximum capacity of your battery as a percentage of its original capacity. Anything above 80 percent is normal. Below 80 percent means the battery is aging.

Check battery health on iPhone

Open the Settings app and tap "Battery". Then tap "Battery Health & Charging". You will see a number labeled "Maximum Capacity" — this is the percentage of the battery's original charge that it can still hold. A new iPhone shows 100 percent. If yours shows 80 percent or higher, the battery is still in good shape. If it shows between 50 and 80 percent, the battery is aging noticeably. If it shows below 50 percent, Apple recommends having the battery replaced.

Below the maximum capacity, you may also see a line that says "Battery Health Management is on" or "Battery Health Management is off". This is a feature that slows down your phone slightly to reduce battery wear — it is safe to leave on, and turning it off will make your battery degrade faster.

Check battery health on Android

Android does not have a built-in battery health screen like iPhone does, but you can see some information by dialing a hidden code. Open the Phone app and dial *#*#4636#*#* — the screen will change to show "Testing" at the top. Tap "Battery Information". You will see your current battery percentage, temperature, and voltage. A healthy battery at room temperature should show a voltage between 4.0 and 4.3 volts. If the voltage is much lower, the battery is aging.

This method does not show you the maximum capacity like iPhone does, so it is less precise. If you want a clearer picture, download a free app like "AccuBattery" from the Google Play Store. Open it and let it run while you use your phone normally for a few days — it will estimate your battery's maximum capacity by measuring how much charge it gains and loses over time.

Physical signs your battery is failing

Before you check any numbers, look at your device itself. If the battery is visibly swollen — the back of your phone is bulging, your laptop keyboard is pushing up, or the screen is separating from the frame — stop using the device immediately. A swollen battery can catch fire or explode. Do not try to open it yourself. Take it to an Apple Store, a Samsung service center, or a certified repair shop right away.

If you see cracks in the battery casing, liquid leaking from the device, a burning smell, or the device getting extremely hot during normal use, these are also signs of a failing or damaged battery. Unplug the device, do not use it, and take it to a repair shop or the manufacturer. These are safety hazards.

If your device shuts down suddenly even though the battery percentage shows 30 or 40 percent, that is also a sign the battery is failing. The percentage reading becomes unreliable as batteries age, so the device may actually be nearly empty even though the screen says otherwise.

What to do if your battery is failing

If your battery health is below 50 percent on iPhone or Mac, or below 50 percent on Windows, you have a few options. The cheapest is to use your device plugged in most of the time — this stops the battery from draining further and lets you keep using the device. The downside is you lose portability.

The most reliable fix is to have the battery replaced. Apple charges between $69 and $199 depending on the model. Most Android phone makers charge $50 to $150. Windows laptop battery replacement costs $100 to $300 depending on the model. You can go to the manufacturer's official store or a certified repair shop. Avoid very cheap third-party repairs — cheap batteries degrade faster and can be unsafe.

If your device is very old and the battery replacement costs more than half the price of a new device, it may be time to replace the whole device instead.

Frequently Asked Questions

Why does my battery percentage jump from 30 to 0 suddenly?

An aging battery cannot accurately report how much charge it has left. The percentage reading becomes unreliable, so your device may show 30 percent when it is actually nearly empty. This is a sign the battery needs replacement soon. Until then, charge your device more often to avoid unexpected shutdowns.

Is it bad to leave my phone plugged in overnight?

Modern phones and laptops stop charging once they reach 100 percent, so leaving them plugged in overnight does not damage the battery. However, keeping a battery at 100 percent constantly does cause it to age slightly faster over months and years. If you want to extend battery life, unplug once it reaches full charge.

Can I replace the battery myself?

On most modern phones and laptops, the battery is glued or soldered in place, making self-replacement difficult and risky. You can damage other components, void your warranty, or hurt yourself. A professional repair shop has the right tools and replacement parts. It is worth the cost.

What does "Battery Health Management" on iPhone mean?

This feature slows down your phone slightly when the battery is aging to reduce wear and extend its lifespan. It is safe and actually helps your battery last longer. You can turn it off in Settings > Battery > Battery Health & Charging, but your battery will degrade faster if you do.

Is a battery at 80 percent capacity still usable?

Yes. A battery at 80 percent capacity is still considered healthy and will power your device through a normal day of use. Most people do not need to replace a battery until it drops below 50 percent or the device starts shutting down unexpectedly.