Separate active use from idle or sleep use
Write down when the loss happens. Is the Mac being used, sitting unlocked, closed in a bag, or asleep overnight? Compare similar periods rather than comparing a video call with an idle afternoon. On a laptop, Activity Monitor shows the battery level over the last 12 hours and an app's 12-hour power measure, which can add useful context.
Energy Impact is a relative, current measure. It is useful for finding a process worth examining, but it is not a direct reading of watts or a prediction of how much battery a process will consume tomorrow.
Inspect active apps before changing anything
Click the battery icon in the menu bar to check the apps listed under Using Significant Energy. This is a quick view of current activity, not a history assigning overnight battery loss to apps. For more detail, open Activity Monitor’s Energy pane and inspect Energy Impact and Preventing Sleep. Identify unfamiliar processes before force-quitting them. Closing an unneeded app is a useful test; deleting software or changing low-level power settings is not a first diagnostic step.
Check the same period on more than one day. A photo import, cloud synchronization, large download, external display, or resource-intensive browser tab may be legitimate short-term activity. The question is whether the same workload remains unusually active after the expected work is complete.
Test one likely cause
Create a baseline from several comparable battery sessions. Make one reversible change, such as quitting one app, unplugging one display, or avoiding one browser workflow. Recheck under similar brightness, network, and workload conditions. If the result changes, repeat once before treating it as a useful finding.
WattGuard groups related processes and estimates impact from activity such as CPU, wakeups, and disk use. Where macOS exposes energy counters it can show measured power, but it cannot turn every process into an exact watt or battery-percentage reading. Use it to prioritize a test, then compare the observed session.
Include battery condition
Battery condition is separate from current energy use. Check it in System Settings. If the condition indicates service is recommended, normal workloads may yield noticeably shorter runtime. If condition is normal but the pattern changed suddenly, keep the baseline notes and investigate the workload or sleep behavior that changed.