C# Signature:

[DllImport("kernel32.dll")]
static extern bool GetSystemPowerStatus(out SYSTEM_POWER_STATUS
   lpSystemPowerStatus);

User-Defined Types:

SYSTEM_POWER_STATUS

Notes:

None.

Tips & Tricks:

Please add some!

Sample Code:

// C# Example by Matt Henry (henrym@sytexinc.com) //

using System;
using System.Runtime.InteropServices; // Necessary!

namespace MyNamespace
{
    /// <summary>
    /// Summary description for BatteryChecker.
    /// </summary>
    public class BatteryChecker
    {
        public BatteryChecker()
        {
            // Nothing
        }

        [DllImport("Kernel32")]
        private static extern Boolean GetSystemPowerStatus( SystemPowerStatus sps );

        public static SystemPowerStatus GetSystemPowerStatus()
        {
            SystemPowerStatus sps = new SystemPowerStatus();
            GetSystemPowerStatus( sps );
            return sps;
        }
    }

    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
    }

    // Fields must mirror their unmanaged counterparts, in order
    [StructLayout( LayoutKind.Sequential )]
    public class SystemPowerStatus
    {
        public ACLineStatus _ACLineStatus;
        public BatteryFlag  _BatteryFlag;
        public Byte     _BatteryLifePercent;
        public Byte     _Reserved1;
        public Int32    _BatteryLifeTime;
        public Int32    _BatteryFullLifeTime;
    }
}

Sample Code:

// C# Example by Matt Wise (matt.wise@narfsoft.com) //

// There is not much functional diffrence between the above example, this would just be simpler class to implement.

using System;
using System.Runtime.InteropServices;

class SystemPower
{
    [DllImport("kernel32.dll", SetLastError = true)]
    private static extern Boolean GetSystemPowerStatus(out SystemPowerStatus sps);

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

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

    private struct SystemPowerStatus
    {
    public ACLineStatus LineStatus;
    public BatteryFlag flgBattery;
    public Byte BatteryLifePercent;
    public Byte Reserved1;
    public Int32 BatteryLifeTime;
    public Int32 BatteryFullLifeTime;
    }

    /// <summary>
    /// Returns true if a an AC Power Line is detected
    /// </summary>
    public static Boolean ACPowerPluggedIn()
    {
    SystemPowerStatus SPS = new SystemPowerStatus();
    GetSystemPowerStatus(out SPS);

    if (SPS.LineStatus == ACLineStatus.Online)
    {
        return true;
    }
    else
    {
        return false;
    }
    }

    /// <summary>
    /// Returns an integer representing the percent of battery charge remaining.
    /// </summary>
    public static Int32 BatteryCharge()
    {
    SystemPowerStatus SPS = new SystemPowerStatus();
    GetSystemPowerStatus(out SPS);

    return (Int32)SPS.BatteryLifePercent;
    }
}

Alternative Managed API:

System.Windows.Forms.PowerStatus