Surface battery drains quickly

1. Open Settings > System > Power & battery and look at battery usage by app.
2. Lower screen brightness and use a power mode that favors battery when you are unplugged.
3. Update Windows and the Surface firmware through Windows Update. Battery fixes often arrive there.
4. Generate a battery report by running powercfg /batteryreport from a terminal, then open the saved HTML file and compare design capacity with full charge capacity.

If full charge capacity is far below the design capacity and the device is several years old, the battery is worn. A worn battery is a hardware limit, not a setting.