As the others have said, it's not that your value in the CSV file is "wrong"; rather it is that Excel is choosing to apply its own formatting to the cell in which you want it to put the value 200802251655. ( OK, I am making an assumption here about your situation.)

I had a situation where I was doing a very similar thing, and my consumers (who were picking up the CSV file in Internet Explorer) were reporting this problem. They did not want to have to go into Excel's "Format Cell..." dialogue. Eventually I changed the format of the generated date/timestamp in the CSV file to "2008-02-25 16:55" (complete with the quotes) , Excel was happy, users were happy, I was happy ;-)