Battery Checker
Level, Drain Rate, Health & Leak Test

What This Battery Checker Actually Measures

This is a battery checker online that reads your device through one small browser interface called the Battery Status API. It returns four values and nothing else: your battery level, whether you are charging, an estimate of time to full, and an estimate of time to empty. Everything on the panel above is either one of those four numbers or something worked out from watching them change.

That matters, because it draws a hard line through what any battery checker in a browser can honestly tell you:

If you searched for a battery health checker online, that right-hand column is the honest answer, and it is why the health section further down sends you to your operating system instead of pretending. Plenty of pages promise a browser-based battery health check and then quietly show you the charge level. This one does not.

What the tool adds on top of the four values

• A measured drain rate. The four values are a snapshot. Watching them over several minutes gives a real percent-per-hour figure, fitted across every reading rather than taken from the first and last.
• Your browser's reporting step. Chromium rounds the level, and some hardened browsers round much harder. The tool works out your step size from your own readings, which is the difference between “this tool is stuck” and “your browser only reports whole percentages”.
• A second opinion on time remaining. Your system publishes an estimate. The tool computes its own and tells you which is more trustworthy right now, and why.
• The raw response. All four values exactly as returned, unrounded and unedited, so nothing here has to be taken on faith.

Which browsers this works in

Support is narrow and it is narrow on purpose.

If the panel above told you your browser does not expose battery data, that is not a fault on this page and there is no setting to turn on. It is a decision the browser vendor made, and the per-device instructions below get you the same information — and more of it — directly from your operating system.

How to Read Your Result

The panel shows more than a percentage, and a few of the numbers are worth explaining because no other battery status checker displays them.

Charge level and state

The large figure is your battery percentage. Every battery percentage check online will show you that number; this one also sorts it into a state, using thresholds device makers set rather than ones we picked. The thresholds are the ones device makers use rather than ones we picked: 20% is where both iOS and Android raise a low-battery warning, and 80% is the top of the range Apple, Samsung and Google all recommend staying inside for longevity.

Reporting step — the tile nobody else has

This is the one that resolves the most common complaint about every battery level checker online: that it seems frozen. It usually is not. Chromium rounds the reported level to the nearest whole percent, so on a laptop that drains at four percent an hour the number legitimately does not move for fifteen minutes.

The tool watches the distinct values your browser reports and works out the smallest real gap between them. That gap is your step size, and it tells you something useful:

• 1% — standard Chromium. What almost everyone will see.
• 5% or coarser — a privacy-hardened browser rounding harder than Chromium does, which also means any short-session estimate here will be jumpy.
• Finer than 1% — unusual today, and worth knowing about, because that extra precision is exactly what made battery readings identifying in the first place.

The tile stays blank until your level actually changes, because until then there is no evidence to measure and guessing would defeat the point.

Raw API values

The dark panel prints the four properties exactly as your browser returned them, with no rounding of ours applied. If you are a developer checking what navigator.getBattery() gives you on a particular device, that panel is the answer. If you are not, it is still the proof that the friendly numbers above it were not invented.

chargingTime and dischargingTime both return Infinity a lot of the time, and that is correct behaviour rather than a bug. A device that is discharging has no time-to-full, so chargingTime is infinite; the reverse is true while charging. Both can also be infinite briefly after you plug in, while the system works out a new estimate.

Drain Rate, Charging Speed and Two Different Time Estimates

A snapshot tells you where you are. A rate tells you where you are heading, which is what most people actually want from a battery life checker online.

How the drain rate is measured

The tool records every level it sees, with a timestamp, and fits a line through the whole set. That matters more than it sounds: with 1% rounding, taking the first and last reading would let one rounding step swing the answer wildly over a short session. Fitting across every point averages that out.

You get a signed figure in percent per hour — a discharge rate while unplugged, a charge rate while plugged in. Leave the tab open for ten minutes before treating it as solid. Under about five minutes, with whole-percent rounding, there simply has not been enough change to fit a line to.

Charging speed

Plugged in, the same measurement turns this into a battery charge checker online. Most tools stop at telling you that you are charging; this one tells you how fast, which is the part that actually diagnoses a bad cable. The tool sorts the rate into a class, and the boundaries come from what real chargers achieve rather than from marketing:

If you plug in and see barely gaining, the cable or the port is the first thing to check, not the battery. A laptop rendering video on a 30W phone charger can genuinely lose ground while plugged in.

Why there are two time estimates, and which to believe

Your operating system publishes its own guess at time remaining, and the tool computes one from the rate it has measured. When they differ, most tools print both and leave you to it. The difference is actually informative:

• They agree. Your workload has been steady. Either number is fine.
• The measured figure is shorter. Your workload got heavier recently. The system averages over a long window and has not caught up, so trust the measured one.
• The measured figure is longer. Your workload got lighter. The system is still averaging in the earlier, heavier period.
• You have been here under ten minutes. Trust the system. A single rounding step looks like an enormous rate change over a few minutes, and the tool says so rather than presenting a wild number as fact.

The panel above states which of these applies to you in plain words as it happens.

The graph and the session log

The chart plots your level against time for the current session, with the 20–80% band shaded so you can see at a glance whether you are inside it. The dashed lines sit at exactly 20% and 80% rather than approximately, which sounds pedantic and is the difference between a chart you can read numbers off and a decoration.

Underneath, the event log timestamps every level change and every time you plug or unplug. Copy session as CSV puts the whole thing on your clipboard — the sample series and the events — which is a genuinely useful thing to attach to a warranty claim or a bug report when you need to show that a device lost forty percent in an hour.

Battery Health: The Number Browsers Are Not Allowed to Show

Charge level tells you how full the tank is. Battery health tells you how big the tank still is compared with the day you bought it, and those are completely different questions. Almost everyone searching for a battery health checker online wants the second one.

People ask for this in a dozen ways. A battery health checker online, free or paid. A battery capacity checker online. A battery health and life checker. A mobile battery health check online when it is a phone rather than a laptop. Every one of those is the same question, and it has one answer.

No browser will give it to you. Capacity, wear and cycle count are far more identifying than a charge level — a specific design capacity paired with a specific current capacity and cycle count is close to a serial number — so the browser engines simply do not expose them. Any site offering a browser-based battery health check is showing you the charge level with a different label on it.

Your operating system does know, and every route below takes under a minute. The panel above opens on your own platform automatically.

What the numbers mean once you have them

Two figures matter, and they answer different questions.

Between them they are what a battery health and life checker online would need to show, and cycle count is the better predictor of the two, because capacity readings are noisy. Apple's own support forums are full of people watching Maximum Capacity fall ten points and then climb back — the figure is an estimate, it is not linear, and obsessing over a single reading is not worth the anxiety. A count of 180 cycles on a two-year-old phone tells you far more than 88% did.

A rough guide when you are judging a device rather than diagnosing one:

• 90% and above — effectively as new.
• 85–89% — normal after a year or two. Nothing to do.
• 80–84% — noticeably shorter days. A replacement is on the horizon.
• Below 80% — considered consumed. On an iPhone this is also where iOS may start managing peak performance to prevent shutdowns.

Buying or selling a used device

Battery health is the first thing to check on a second-hand phone or laptop, and it is the easiest thing for a listing to misrepresent. Read the figure on the device itself rather than from a screenshot, which takes seconds to fake. On an iPhone that is Settings → Battery → Battery Health & Charging; on a Mac, hold Option and click the Apple menu, then System Information → Power.

Anything at 85% or above is fair. Below 80% you are buying a battery replacement along with the device, so price it accordingly rather than walking away — a swap is usually far cheaper than the discount it justifies.

Checking a Laptop, Phone, iPhone or Tablet

The tool behaves differently depending on what you opened it on, and it is worth knowing why before you conclude something is broken.

Laptop

As a laptop battery checker online, this works fully in Chrome, Edge, Opera and other Chromium browsers on Windows, macOS, Linux and ChromeOS. You will get the live level, the measured drain rate and the graph. Leave the tab open while you work normally for the most useful reading — a rate measured while the machine idles on a settings page tells you nothing about your actual day.

A battery health check laptop owners can act on has to come from the operating system, and Windows happens to have the best built-in tool of any platform. powercfg /batteryreport writes an HTML file containing design capacity, full charge capacity, a usage history, and — the part almost nobody knows about — a comparison of what Windows estimated your runtime would be against what it actually was. If your laptop dies earlier than the taskbar promises, that table is where the evidence lives.

Android phone

As a phone battery checker online, Chrome for Android and Samsung Internet both work. The reading is the same one the status bar shows, so the value here is the rate and the graph rather than the percentage.

There is no battery health check online that works on Android, and no consistent offline one either, because Google has never required manufacturers to expose health at all. Samsung Members has a proper diagnostic; Pixels on Android 14 and later have a Battery health entry in Settings; everything else falls back to the *#*#4636#*#* testing menu — the battery health check code people pass around — which many recent builds have quietly disabled. AccuBattery is the reliable fallback, but it learns your capacity by watching a few charge cycles, so it needs a couple of days before its estimate means anything.

iPhone and iPad

This is the case that trips people up, so plainly: no browser on an iPhone or iPad can read your battery. Safari has never implemented the API, and Apple requires every iOS browser to use WebKit underneath, so Chrome, Edge, Firefox and Brave on iOS all inherit the same gap. An iPhone battery checker online that claims to show your level on iOS is not reading your battery. Nor is the free version of one — the limit is Apple's, not the tool's, so no web page gets past it.

Apple's own screen is better than anything a web page could offer anyway. Settings → Battery → Battery Health & Charging gives you Maximum Capacity, whether a replacement is recommended, and on iOS 17 and later the cycle count, the manufacture date and the date of first use. Nothing on the web comes close to that.

Desktop with no battery

A mains-powered desktop returns a full, charging battery with no time estimates, because that is the sensible thing for the API to say when there is nothing to report. The tool will show 100% and flag that it cannot tell this apart from a browser substituting values, which is covered in the privacy section below.

Why Your Battery Is Draining Fast

If the rate above is worse than you expected, capacity wear is rarely the reason. Wear is gradual — a few percent over a year. Sudden fast drain almost always has a specific and fixable cause, and the graph makes it easy to test each one: note the rate, change one thing, watch what the rate does over the next ten minutes.

Cold deserves a note because it frightens people. Lithium chemistry slows in the cold, so a phone can drop twenty points walking to the shops in winter and then recover most of it indoors. That is not damage and it is not a failing battery. Heat is the one to worry about, and it is covered next.

If a laptop dies well before Windows says it should, run the powercfg report from the panel above and look for the section comparing estimated against observed runtime. A large, consistent gap there is a real finding you can take to a manufacturer.

What Actually Makes a Battery Last

There is more folklore about battery care than almost any other topic in consumer technology, and a good deal of it is left over from a chemistry that has not been used in phones for twenty years. Here is what the evidence supports.

Heat is the biggest factor, not your charging habits

This is the part most advice buries. Temperature drives the chemical reactions that age a cell, so it accelerates degradation regardless of how carefully you manage charge levels. A battery kept cool at 100% can comfortably outlast one kept at 50% in a hot car.

Practically: take the case off if the device gets hot while fast charging, do not leave anything in a parked car or in direct sun, and avoid gaming while plugged in, which is the worst combination of heat sources a phone routinely encounters.

The 20–80% rule is real but oversold

The reasoning is sound. At high states of charge the internal voltage peaks and lithium can plate onto the anode instead of embedding into it, which permanently removes it from circulation. At very low charge the electrolyte comes under a different kind of stress. The middle of the range is genuinely gentler, and going from 80% to 100% does disproportionately more damage than going from 30% to 50%.

But modern devices already manage this for you. Optimised charging on iOS, adaptive charging on Pixel and the 80% cap on recent iPhones and many laptops all exist to hold the cell out of the top of the range when it does not need to be there. Turning those on is worth more than watching a number yourself. Draining to 3% every day is worth avoiding; charging to 100% before a flight is not worth a second thought.

Three things that are simply myths

• “Fully discharge it occasionally to calibrate.” This is left over from nickel-cadmium cells and their memory effect. Lithium-ion has no memory effect, and deep discharge is one of the two states that actually stresses the chemistry.
• “Overnight charging kills the battery.” A device at 100% on a charger stops drawing current. The mild cost is sitting at a high state of charge for hours, which is exactly what optimised charging exists to avoid — it holds at 80% and finishes shortly before your alarm.
• “Only use the original charger.” Charging is negotiated between the device and the supply. A reputable third-party charger delivering the right standard is fine. A no-brand one that ignores the negotiation is not, and that is a safety point rather than a longevity one.

The Battery Leak Test: Is Your Battery Status Exposed to Websites?

The panel at the top of this page answers one question before any of the others: can a website read your battery at all? That is the battery leak test, and it gives you one of three verdicts.

If you got the first verdict, that is the best outcome and there is nothing to fix. Most tools frame a missing API as a failure and apologise for it. It is not a failure — it is the browser doing exactly what you would want.

What is actually exposed when it is readable

There is no permission prompt for this. Any page you open can call navigator.getBattery() and read four values, and the breakdown table in the panel shows yours alongside what each one gives away. That is what battery API fingerprinting is built from, and how battery feeds into a wider device fingerprint: not one value, but the combination, and the fact that it changes slowly enough to stay recognisable for the half hour you spend browsing.

The concern is not that a site learns you are at 67%. It is that cross-site tracking becomes possible without cookies — two unrelated pages reading the same unusual combination within a few minutes can reasonably conclude they have the same visitor. That survives incognito, and it survives a VPN, because the data comes from your hardware rather than your connection.

Can a website really track me through my battery?

It could, and the demonstration is what changed the browsers. The concern applies equally to a laptop battery and a phone battery — arguably more to a laptop, because the level moves in smaller, more distinctive steps.

What has changed is the scale. With the rounding Chromium now applies, the panel above measures your reading at roughly eight bits, which narrows a thousand visitors to a handful rather than singling you out. Before that rounding existed the same calculation gives about fifteen bits, which is effectively unique. That gap is the whole story of what the defence bought.

How to stop your battery status being exposed

• Firefox removed the API in 2017. There is nothing to configure.
• Safari never shipped it, on any Apple platform.
• Brave and Tor Browser substitute a fixed value, so every user of them looks the same.
• Chrome, Edge and Opera expose it with rounding applied, and offer no setting to disable it. An extension can override navigator.getBattery, though that is a heavier fix than most people need for eight bits.

Worth keeping in proportion. Battery is one signal among dozens, and on its own it is one of the weaker ones now. Your canvas fingerprint and your font list both give away considerably more. If the reason you are here is tracking rather than charge level, the full browser leak test is the more useful page, because it measures the combination rather than one input at a time.

Why Browsers Restricted Battery Data in the First Place

The reason a battery checker can read so little is worth understanding, because it explains every limitation on this page.

Battery is one of a family of hardware signals a page can read without asking — CPU core count, memory estimate and screen dimensions sit alongside it, all visible in the browser info tool. The W3C published the Battery Status API in 2012 with a reasonable goal: let a page notice you are low and do less work. The specification exposed the level as a full-precision number and the time estimates to the second, and stated that the privacy impact was minimal.

It was not. In 2015 researchers demonstrated that the precise level combined with the discharging time formed a short-lived but near-unique identifier — two sites reading it within a few minutes could tell they had the same visitor, with no cookies, through incognito, and behind a VPN, because the data comes from your hardware rather than your connection. Firefox removed the API entirely in 2017. WebKit never shipped it. Chromium kept it and rounded the values instead.

What it is worth today, with actual arithmetic

Every privacy page will tell you battery data is “high risk”. The panel above does the sum instead, because the rounding changed the answer considerably.

With Chromium's whole-percent rounding, the level has around a hundred possible values, charging is a single bit, and the time estimates are bucketed. There is a second effect most analyses miss: time remaining is largely determined by the level, so treating the two as independent double-counts. Once you account for that, and for the fact that real battery levels cluster in the middle of the range rather than spreading evenly, the honest figure lands around eight bits.

Eight bits narrows a thousand visitors to a handful. It does not identify you. In 2015, with no rounding at all, the same calculation gives roughly fifteen bits — effectively unique, which is precisely why the defence was introduced. The panel shows both your own figure and what it means in plain numbers.

That is not a reason to dismiss it. Battery data still combines with your canvas fingerprint, your installed fonts and your screen dimensions, and each of those contributes its own bits. The full browser leak audit is the way to see the combination rather than one signal at a time.

The reading this tool refuses to guess about

Tor Browser reports a battery at exactly 100%, charging, with no time estimates — the same values for every user, so nobody stands out. A mains-powered desktop with no battery reports exactly the same four values.

From JavaScript those two cases are identical. There is no test that separates them. So when the panel above sees that signature it says it cannot tell, rather than declaring “spoofed detected” and being wrong for every desktop user who visits. Other tools guess. We would rather be useful than confident.

If you are on a laptop or phone that is plainly not full and you see 100%, your browser is substituting the value on purpose. That is the feature working.

Frequently asked questions about checking your battery