Maintain User Entered Text In TextBox

I have an ASP.Net UpdatePanel that updates on a timer. Within the UpdatePanel and nested in a GridView, I have a TextBox that the user enters a value in with a submit button. Everything works fine, except if the user does not submit the value before the timed interval, the text is removed from the TextBox. Is there a way to persist the user entry into the TextBox between updates? Is there a better way of doing this?

Code Postscript:
aspx:
<script type="text/javascript">
var prm = Sys.WebForms.PageRequestManager.getInstance();
prm.add_beginRequest(beginRequest);
function beginRequest() {
prm._scrollPosition = null;
}
</script>
<asp:Timer ID="Timer1" runat="server" Interval="900" OnTick="Timer1_Tick"></asp:Timer>
<asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="Conditional">
<Triggers>
<asp:AsyncPostBackTrigger ControlID="Timer1" EventName="Tick" />
</Triggers>
<ContentTemplate>
<asp:DataList RepeatColumns="5" RepeatDirection="Horizontal" ID="dlMine" runat="server" OnItemCommand="Item_Command">
<ItemTemplate>
<div style="border:1px solid black;margin:3px;height:300px;text-align:center;padding:5px;">
<div style="width:150px;">
<asp:Label ID="lblTitle" runat="server" Text='<%# left(DataBinder.Eval(Container.DataItem,"title").ToString(), 75) %>'></asp:Label>
</div>
<asp:Label ID="Label1" runat="server" Text='<%# (DateTime)DataBinder.Eval(Container.DataItem,"end_date") %>'></asp:Label>
<br />
<asp:Label ID="Label2" runat="server" Text='<%# String.Format("{0:C}",DataBinder.Eval(Container.DataItem,"current_value")) %>'></asp:Label>
<br />
<asp:TextBox ID="txtNewValue" runat="server"></asp:TextBox>
<asp:Button Visible='<%# (isInThePast((DateTime)DataBinder.Eval(Container.DataItem,"end_date"))) ? false : true %>' CssClass="bid_button" runat="server" CommandArgument='<%# Eval("ID") %>' CommandName="Revalue" ID="btnBid" Text="Submit New Valuation" />
</div>
</ItemTemplate>
</asp:DataList>

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