BatteryProWatch your laptop or phone battery in the browser: live level, charging state and time remaining, a charge limit with a loud alert when it is reached, a low-battery alert, cycle counting, a usage chart and pattern-based predictions. Readings stay in your browser: nothing is uploaded.
A profile sets the low-battery alert and the charge limit in one click. Keys 1, 2 and 3 pick the first three.
A web page cannot stop the charger itself; the alert tells you when to unplug.
Rules of thumb from the readings this page has seen, not measurements of the battery itself.
One point whenever the level or the charging state changes, at most once a minute. A dashed pink stretch is time the page was closed.
A cycle is counted when the charger is unplugged above half your charge limit while this page is open.
Those browsers report the battery to web pages. The ring fills to the current level and the three readings underneath show whether you are charging, how long the browser expects the charge or the discharge to take, and the health estimate. Firefox and Safari give no readings, so the page shows a simulated battery there and says so.
Conservative (25% to 80%), Balanced (20% to 90%) and Extended (15% to 95%) set both alerts in one click; the plus button saves a custom profile with its own icon. The two sliders in the Charge Limit card do the same by hand, and the limit cannot go below the low-battery threshold.
In the Alerts card keep the low-battery and charge-limit alerts on, choose whether they beep, and click Enable so the browser can show a notification even when the tab is behind another window. The settings button sets the volume, the two beep tones and the threshold; Test plays one so you know what to expect.
Night mode caps the limit at 80% overnight so the battery does not sit full for hours; Weekend mode adds 5% on Saturday and Sunday; Keep the screen awake stops the device sleeping while you monitor; Pattern-based predictions records when you charge so the Assistant can predict your next charge.
Usage history draws the level over time, with dashed pink stretches for the hours the page was closed. Charge cycles counts a cycle each time you unplug above half the limit, by weekday. Insights shows the average level, the cycle count, an efficiency score from the discharge rate, an eco score and a carbon estimate.
CSV writes the level history as a spreadsheet; JSON writes everything, settings and patterns included, and Import merges such a file back, on this computer or another. Settings holds the same buttons plus Clear all data, which removes every reading and setting the tool has stored in this browser.
The battery level, your charging times and your habits say a lot about how you use a computer. This tool has no server side and no account: the readings, the cycle counts, the patterns and the settings live in your browser's storage on your own device, and the only copy that leaves it is the file you export yourself.
When the battery reaches your limit or falls to your threshold, a looping beep starts, a notice appears on the page, the tab title flashes, the tab icon turns into a warning badge and the browser shows a notification if you allowed it. Unplugging or plugging in stops the sound; so does Stop alerts, the notice's button or Alt+X.
A web page cannot cap charging, read the battery's capacity or count the cycles the battery has done in its life. BatteryPro says so on the page and in every label: the health score, the lifespan range and the carbon figure are estimates from what the browser reports and what this tool has seen, and they are named as such.
With predictions on, the tool records the level, hour and weekday every few seconds and the start and end of each charge. After fifty samples it predicts when you usually plug in at this level and weekday, works out your usual charging window, and after a hundred samples classes you from Conservative to Heavy user.
A point is added whenever the level or the charging state changes, at most once a minute, so the usage chart stays readable over days. A break of more than five minutes is drawn as a dashed pink stretch, and its tooltip says how long the page was away, so a flat line is never mistaken for a steady battery.
Export as CSV for a spreadsheet or as JSON for a full backup, import the backup on another computer and the histories merge. Clear all data removes everything the tool stored in this browser in one confirmed click. The old BatteryPro storage from the earlier address is read once and carried over.
Every figure on this page comes from one of two places: a small set of readings the browser passes on from the operating system, or arithmetic this tool does on those readings over time. Knowing which is which tells you how much weight to give each number.
Four things: the charge level as a fraction, whether the charger is connected, the seconds until full while charging, and the seconds until empty while discharging. Chrome, Edge, Opera and the other Chromium browsers provide them on Windows, macOS, Linux, ChromeOS and Android; Firefox and Safari provide none, which is why the page falls back to a simulated battery there. The time estimates are the operating system's own and can be missing for the first minute after plugging or unplugging.
Time remaining when the browser gives none, from the rate the level changed over the last readings. Charge cycles, counted each time the charger is unplugged above half the limit while the page is open. The discharge rate, the average level, the efficiency and eco scores, the health score, the lifespan range and the carbon figure, all from the counted cycles, your limit and the level history. Predictions, from the pattern samples.
The design capacity and the capacity today, the cycle count the battery has done in its life, the cell voltage and temperature, and the charger's power. Those live in the operating system's battery report: on Windows run powercfg /batteryreport in a command prompt; on a Mac hold Option and click the battery icon, or open System Information, Power; on Android most makers show it under Settings, Battery. Use that report for the real wear figure, and this page for day-to-day monitoring and alerts.
Why 80%. A lithium-ion cell ages fastest at the two ends of its range: held near 100% the voltage is at its highest and the chemistry inside degrades quicker, and drained to nearly empty it is stressed in a different way. Keeping the charge between roughly 20% and 80% for everyday use, and going to 100% only when you need the full run time, is the single most effective habit. Laptop makers know this, which is why many offer a "battery health" or "charge threshold" setting in their own software that stops charging at 80%; if yours has one, use it, and use this page's alert for the days you want a different limit or for a device without such a setting.
What a cycle is. One cycle is a full 100% of discharge, in any number of pieces: 50% today and 50% tomorrow is one cycle, not two. Most laptop and phone batteries are rated to keep about 80% of their original capacity after 300 to 500 full cycles, and keep working with less capacity after that; the Assistant's lifespan range of 500 to 1,000 cycles is the wider band in which a battery is usually replaced, nudged up when you keep the limit low and the average level moderate. The cycles this page counts are only the ones it sees while open; the lifetime figure is in the operating system's report.
Heat is the other enemy. A battery that sits at 100% on a charger in a warm laptop, or a phone charging under a pillow, ages faster than one cycled gently at room temperature. Charge on a hard surface, keep the vents clear, avoid charging in direct sun or a hot car, and do not game or render heavy video while plugged in at full charge if you can help it. Night mode exists for the same reason: it keeps the overnight limit at 80% so the battery does not spend seven hours full and warm.
Slow is fine, fast is fine, full is the problem. Fast charging adds a little heat but modern devices manage it well; the wear comes from the time spent near full, not from the speed of getting there. Storing a device for weeks is best done at about 50%, powered off. And a battery that has sat empty for months can refuse to charge at all, so an old laptop in a drawer is better topped up a few times a year.
Reading the time estimates. The browser's time remaining is the operating system's own guess from the current draw, and it swings with what you are doing: it will drop while a video exports and climb again when the machine idles. This page holds a value for a minute and only replaces it when the new one differs by more than a fifth, so the figure does not flicker; when the operating system gives none it falls back to the rate it measured itself. Treat it as a trend, not a countdown.
Using the alert in practice. Leave the tab open in its own window while you work on the charger; when the limit is reached, unplug and the beep stops on its own. The Keep the screen awake switch stops the device sleeping, which would also stop the monitoring. In a background or minimized tab the page takes a fresh reading every five seconds (browsers stop refreshing a hidden page's own battery object, so the page asks a fresh one), the level in the tab title stays current, and the notification and flashing title reach you; the sound needs one click anywhere on the page earlier in the visit, because browsers block audio a page starts on its own.
No. A web page cannot control the charger; only the operating system or the maker's own software can cap charging. BatteryPro watches the level and tells you loudly when it reaches your limit, with a looping beep, a browser notification, a flashing tab title and a notice on the page, so you can unplug at the right moment.
Chrome, Edge, Opera and other Chromium-based browsers on Windows, macOS, Linux, ChromeOS and Android report the battery level, charging state and time estimates to web pages. Firefox and Safari do not, so BatteryPro shows a simulated battery there and says so at the top of the tool; everything else on the page still works.
It is an estimate, not a hardware reading. Browsers do not expose capacity or wear, so the score is built from what the tool can see: how many charge cycles it has counted, how high your charge limit is and how low you tend to let the battery go. For the real capacity use the operating system's battery report.
Yes. In a background or minimized tab the page takes a fresh reading every five seconds, so the level in the tab title stays current and the alert still plays, sends a browser notification and flashes the title. The alert sound needs you to have clicked somewhere on the page once in that visit, because browsers block audio a page starts on its own. A sleeping computer runs no pages, so keep the screen awake while you monitor.
In your browser's storage on this device, under the tool's own name: the readings, cycle counts, usage patterns, profiles and settings. Nothing is sent to a server and there is no account. Export writes it all to a file; Clear all data deletes it.
It is free, with no registration and no limits. Like every page on ZeroDataUpload, it is supported by advertising.