Оформил: DeeCo
Автор: http://www.swissdelphicenter.ch

procedure TForm1.Button1Click(Sender: TObject);
 var
   SysPowerStatus: TSystemPowerStatus;
 begin
   GetSystemPowerStatus(SysPowerStatus);
   if Boolean(SysPowerStatus.ACLineStatus) then
   begin
     ShowMessage('System running on AC.');
   end
   else
   begin
     ShowMessage('System running on battery.');
     ShowMessage(Format('Battery power left: %d percent.', [SysPowerStatus.BatteryLifePercent]));
   end;
 end;