The most boring task I have as a gadget reviewer is testing battery life. First I tediously configure a phone, tablet or laptop to run a few Internet-connected apps and keep its screen on instead of dimming automatically. (To Android vendors who remove that option from Google’s Settings app: Try tapping a mobile device’s screen every 10 minutes for six hours straight, you jerks.) Then I have to sit there until the gadget in question throws up its hands, electronically speaking, and powers down or enters a last-ditch sleep mode.

But on most laptops, I can stop paying attention once I unplug them. That’s because Windows and Mac OS X each automatically log all system events, including low-battery sleep, and make that data reasonably accessible to the user.

In Windows 7 and 8, open the Control Panel (in Windows 10, open the Settings app) and search for “event log,” then click the “View event logs” link. In that app, click the “Windows Logs” category at the left, then its “System” listing. In a second or two, the center of that window will fill with entries.

Click there, hit Ctrl-F to open a search window, and type “Kernel-Power.” Click the search dialog’s “Find Next” button until you spot an entry whose description reads “The system is entering sleep. Sleep Reason: Battery.” That time is when the battery ran out.

On a Mac, the menu bar will show the last time the computer was on for a few seconds  after you power it on again. After that, the following routine applies.

Hit the Apple-icon menu, select “About This Mac” and, in that About window, click its “More Info…” button; in the next window that opens, click “System Report…” That will open the System Information app (formerly known as Apple System Profiler, also available in the Applications folder’s Utilities sub-folder). In its left-hand column, scroll down to the “Software” heading and select “Logs”; from the list that will present in the app’s top-right pane, select “Power Management logs.”

Click in the the pane below that heading, hit Cmd-F and search for “low power sleep”; you should see an entry including that phrase, preceded by a timestamp and followed by a note in parentheses that the battery was at “Charge:0%”

(I don’t expect many of you will need to employ this knowledge. But at least I won’t have to research this stuff all over again the next time I test a laptop.)

Updated 9/14/2016 with Windows 10 instructions.