//声明
GetSystemPowerStatus(
  var lpSystemPowerStatus: TSystemPowerStatus {TSystemPowerStatus 结构}
): BOOL;

//TSystemPowerStatus 是 _SYSTEM_POWER_STATUS 结构的重定义:
_SYSTEM_POWER_STATUS = packed record
  ACLineStatus : Byte;         {0:电源断电; 1:电源正常; 255:电源状态未知}
  BatteryFlag : Byte;          {1:电量充足; 2:电量低; 4:电池基本耗尽; 8:充电; 128:没有电池; 255:电池状态未知}
  BatteryLifePercent : Byte;   {0..100:所剩电量百分数; 255:未知}
  Reserved1 : Byte;            {保留, 须为 0}
  BatteryLifeTime : DWORD;     {电池剩余能量; -1 表示未知}
  BatteryFullLifeTime : DWORD; {电池总能量; -1 表示未知}
end;


//举例:
procedure TForm1.FormCreate(Sender: TObject);
var
  Power: TSystemPowerStatus;
begin
  GetSystemPowerStatus(Power);

  Memo1.Clear;
  with Memo1.Lines do
  begin
    Add(Format('电源状态: %d',[Power.ACLineStatus]));
    Add(Format('电池状态: %d',[Power.BatteryFlag]));
    Add(Format('电量百分比: %d',[Power.BatteryLifePercent]));
    Add(Format('剩余能量: %d',[Power.BatteryLifeTime]));
    Add(Format('总能量: %d',[Power.BatteryFullLifeTime]));
  end;
end;


//效果图: