I tried one of these with my HTC HD7:
http://www.amazon.co....Battery/dp/B004E2RM4C - it was rubbish, and actually performed worse than the original battery!
However, then I tried one of these:
http://www.ecrater.co...tc-hd7-a9292-2x-extra - it was excellent! These batteries last longer because they're bigger - makes sense, really! Of course, they do make that actual device a big bigger and heavier, but not much. It's definitely worth it...
They supply equivalent long-life batteries for the Desire - put "htc desire battery extra" in the search box and find the one which corresponds to your specific model.