Why use this instead of a YouTube timer?
YouTube often pauses long sessions with "Are you still watching?", buffers if your connection drops, and worst of all: when the laptop dies, the YouTube tab is gone and you lose the exact time.
DrainLab plays a lightweight 1080p video loop directly from the browser cache (no continuous bandwidth used) and saves the timer and battery level to your browser every 5 seconds. When the laptop powers back on, your test result is right here.
How the test works
1. Charge your notebook to 100%.
2. Set your screen brightness to 50% and close background software.
3. Unplug the charger and click "Start Battery Test".
4. The Screen Wake Lock API prevents the screen from going to sleep while playing video.
5. Let it run until the notebook completely discharges. Plug it back in, turn it on, and reopen this page to see the exact battery runtime and drain rate.
Frequently asked questions
Does it keep counting after the laptop turns off?
The website saves the elapsed time every 5 seconds in localStorage. When the laptop suddenly shuts down due to battery exhaustion, the last recorded timestamp is saved. When you restart the laptop, it automatically calculates the final runtime.
Why does battery % not show on Safari or Firefox?
The Battery Status API is currently only supported in Chromium browsers (Google Chrome, Microsoft Edge, Opera, Brave). In Firefox or Safari, the timer and shutdown detection work normally, but percentage tracking is unavailable.
Do ads interfere with the battery drain?
No. As soon as you click Start Test, all advertisement slots are completely hidden and halted so they do not impact CPU or battery usage.