Works normally when plugged in but becomes extremely slow on battery

The laptop performs normally on AC power but becomes unusably slow on battery even after power settings change. That points beyond a simple plan choice and may involve firmware, an OEM power-management driver, thermal limits, or a failing battery. Set On battery power mode to Best performance, then compare CPU Speed and the highest CPU process in Task Manager while plugged in and unplugged. Generate powercfg /batteryreport and compare full-charge capacity with design capacity. Install current BIOS, chipset, graphics, and power-management packages from the laptop manufacturer, then applicable Windows updates, and restart. Run the manufacturer’s battery and hardware diagnostics. If CPU speed locks at a very low value only on battery afterward, record the clock speed and battery report and contact the manufacturer. That pattern needs model-specific firmware or hardware diagnosis, not another generic Windows power-plan change.