I have used the sample here and did little modifcations
ASP.Net : Google Maps V3 with Multiple Markers Database Example
HTML
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
</head>
<body>
    <form id="form1" runat="server">
    <script type="text/javascript" src="http://maps.googleapis.com/maps/api/js?sensor=false"></script>
    <script type="text/javascript">
    var markers = [
    <asp:Repeater ID="rptMarkers" runat="server">
    <ItemTemplate>
             {
                "title": '<%# Eval("Name") %>',
                "lat": '<%# Eval("Latitude") %>',
                "lng": '<%# Eval("Longitude") %>',
                "description": '<%# Eval("Description") %>'
            }
    </ItemTemplate>
    <SeparatorTemplate>
        ,
    </SeparatorTemplate>
    </asp:Repeater>
    ];
    </script>
    <script type="text/javascript">
        window.onload = function () {
            for (i = 0; i < markers.length; i++) {
                var mapOptions = {
                    center: new google.maps.LatLng(markers[0].lat, markers[0].lng),
                    zoom: 6,
                    mapTypeId: google.maps.MapTypeId.ROADMAP
                };
                var infoWindow = new google.maps.InfoWindow();
                var map = new google.maps.Map(document.getElementById("dvMap" + (i + 1)), mapOptions);
                var data = markers[i];
                var myLatlng = new google.maps.LatLng(data.lat, data.lng);
                var marker = new google.maps.Marker({
                    position: myLatlng,
                    map: map,
                    title: data.title
                });
                (function (marker, data) {
                    google.maps.event.addListener(marker, "click", function (e) {
                        infoWindow.setContent(data.description);
                        infoWindow.open(map, marker);
                    });
                })(marker, data);
            }
        }
    </script>
    <asp:Repeater ID="rptMaps" runat="server">
        <ItemTemplate>
            <div id='dvMap<%# Container.ItemIndex + 1 %>' style="width: 400px; height: 200px">
            </div>
        </ItemTemplate>
        <SeparatorTemplate>
            <hr />
        </SeparatorTemplate>
    </asp:Repeater>
    </form>
</body>
</html>
Code
 protected void Page_Load(object sender, EventArgs e)
    {
        if (!this.IsPostBack)
        {
            DataTable dt = this.GetData("select * from Locations");
            rptMarkers.DataSource = dt;
            rptMarkers.DataBind();
            rptMaps.DataSource = dt;
            rptMaps.DataBind();
        }
    }
    private DataTable GetData(string query)
    {
        string conString = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
        SqlCommand cmd = new SqlCommand(query);
        using (SqlConnection con = new SqlConnection(conString))
        {
            using (SqlDataAdapter sda = new SqlDataAdapter())
            {
                cmd.Connection = con;
                sda.SelectCommand = cmd;
                using (DataTable dt = new DataTable())
                {
                    sda.Fill(dt);
                    return dt;
                }
            }
        }
    }
