How do I find what's draining my MacBook battery?

Open Activity Monitor from Applications > Utilities, click the “Energy” tab, and sort by “Energy Impact.” Look for anything using more than 20 when you’re not doing obvious work — Chrome, Zoom, and Slack are common culprits. Kill those, and your battery should settle down. If nothing stands out, check if Spotlight is re-indexing or a rogue widget is the problem.