I ran Windows' hidden power report and found exactly why my battery was dying

When a Windows laptop starts draining battery faster than usual, most people check Task Manager first. That works well for obvious problems like an app hammering the CPU, but plenty of power issues happen lower down. A USB device might refuse to power down, an app might keep requesting a high-resolution system timer, or your power plan might be configured in a way that keeps hardware running harder than it needs to.