Question

How to detect (from Delphi) when the laptop is running on batteries (or AC)?

Answer 1

To be notified when the status changes on Vista and Windows 7 you can use RegisterPowerSettingNotification.

For Windows 2000 and later, look at GetSystemPowerStatus, or go to MSDN and read about Power Management.

(Someone always posts while I am typing 🙁 )

function GetBattery : Boolean;
var
  SysPowerStatus: TSystemPowerStatus;
begin
  Win32Check(GetSystemPowerStatus(SysPowerStatus));
  case SysPowerStatus.ACLineStatus of
    0: Result := False;
    1: begin
      Result := True;
      // You can return life with
      // String := Format('Battery power left: %u percent.', SysPowerStatus.BatteryLifePercent]);
    end;
    else
      raise Exception.Create('Unknown battery status');
  end;
end;