How to compare battery drain at 30% and 70%

Does your battery seem to drain faster at 30% than at 70%? A fair comparison can show whether the difference repeats, or whether it came from a change in screen brightness, apps, or workload.

Use the Battery Meter to check the charge level, charging state, time left, and drain rate. Compare two timed sessions on the same device, one near 70% and one near 30%.

Compare drain at 70% and 30%

1. Open the Battery Meter on the device you want to check. It appears only if your device and browser report battery information. If it does not appear, that is a browser or device limitation, not proof the battery is faulty.
2. At about 70%, unplug the device and check that the charging state shows it is no longer charging. Note the charge level and drain rate. Use the device in a repeatable way for 20 minutes, then note the level and rate again. If the percentage barely changes, extend the session to 30 minutes.
3. Let the battery reach about 30% through normal use. Then repeat the same timed session with the same screen brightness, apps, network connection, and workload. Note the starting and ending levels and the drain rate.
4. Compare the two sessions. If the tool's reported rate changes during a session, use the starting and ending levels to calculate the average: starting percentage minus ending percentage, divided by the number of minutes.

For example, a drop from 70% to 68% over 20 minutes is 0.1 percentage points per minute. Write down the results rather than relying on memory. The displayed percentage is rounded, so a short session can make the rate look uneven.

What the result means

The rates are close

Your device used a similar amount of charge per displayed percentage point in both sessions. Small differences are normal, especially if a background task ran or the meter updated its estimate.

The rate is higher at 30%

This can happen when the device changes its power behavior at a lower charge, or when the remaining-charge estimate shifts. Check whether Battery Saver or Low Power Mode turned on. One comparison does not show that the battery has lost capacity.

The rate is higher at 70%

Look for differences in workload first. A video call, update, bright screen, or busy app can use more power than a quiet desktop. Repeat the sessions under matched conditions before drawing a conclusion.

The level drops in jumps or the rate changes sharply

Battery meters use estimates, and the displayed percentage may stay still and then move by a point. Repeat the comparison for longer. If the level repeatedly falls by several points at once or the device shuts down while it still reports charge, check the operating system's battery health information or ask a repair shop to test it.

Make the comparison fair

1. Use the same workload. Choose an activity you can repeat, such as playing the same video at the same resolution or keeping the same set of work apps open. Do not run a heavy benchmark in one session and browse lightly in the other.
2. Match screen brightness. On Windows 11, go to Settings › System › Display. On a Mac, open System Settings › Displays. On an iPhone, use Settings › Display & Brightness. On Android, open Settings › Display; the exact label can vary by device.
3. Keep power-saving settings consistent. On Windows 11, check Settings › System › Power & battery. On a Mac, check System Settings › Battery. On an iPhone, check Settings › Battery › Low Power Mode. On Android, check Settings › Battery for Battery Saver or a similar option. If the device automatically changes modes near 30%, note that in your results rather than treating the sessions as identical.
4. Keep the device in a similar environment. Avoid comparing a cool room with a hot one, or a quiet idle session with one that has updates running. Heat and background activity can change power use.
5. Repeat a surprising result. Run each session again if practical. If the difference appears only once, it may reflect a temporary task or a rounded battery reading.

What this comparison cannot tell you

The drain rate describes how quickly the displayed charge falls under the conditions you tested. It is not a direct measurement of battery capacity, wear, or health. Battery percentages are estimates, and a percentage point does not always represent exactly the same amount of energy at every charge level.

For more on the difference between current drain and battery wear, see why battery wear and current discharge rate differ. If your device reports no battery data in the browser, use its built-in battery settings or a manufacturer diagnostic instead.