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;