C#

<br />
[DllImport("user32.dll", SetLastError=true)]<br />
static extern IntPtr PrintWindow(IntPtr hwnd, IntPtr hDC, uint nFlags);<br />

[DllImport("Kernel32")]
private static extern Boolean GetSystemPowerStatus(SystemPowerStatus sps);
[StructLayout(LayoutKind.Sequential)]
public class SystemPowerStatus
{
        public ACLineStatus _ACLineStatus;
        public BatteryFlag  _BatteryFlag;
        public Byte         _BatteryLifePercent;
        public Byte         _Reserved1;
        public Int32        _BatteryLifeTime;
        public Int32        _BatteryFullLifeTime;
}

public enum ACLineStatus : byte
{
    Offline = 0, Online = 1, Unknown = 255
}

public enum BatteryFlag : byte
{
        High = 1,
        Low = 2,
        Critical = 4,
        Charging = 8,
        NoSystemBattery = 128,
        Unknown = 255
}

private void button1_Click(object sender, EventArgs e)
{
    SystemPowerStatus sps = new SystemPowerStatus();
    GetSystemPowerStatus(sps);
    if (sps != null)
    {
        MessageBox.Show(string.Format("Current battery life is at {0}%.", sps._BatteryLifePercent));
    }
}