The HTC Desire was fine for us when it came to lasting a day, but others found it would be dead by 7PM. The Desire HD was more universally panned for a poor battery, but still some chastised our verdict of it being unacceptable.
Well, it's going to happen again with the HTC Sensation, as the battery life, to us, seems woeful and not up to scratch. We're talking dead by 8PM with no push email, minimal Wi-Fi and about 30 mins of music and video at the most.
We've cycled it a few times to see if it can be improved, but the same things happens: it holds charge averagely well mostly, but then will get very warm and discharge at a rate of 10% per hour... which is a familiar scenario with the Desire HD.
We constantly kept the applications killed and the notifications to a minimum - but it seems only turning off the background synchronisation altogether helped the issue. And don't even think about hammering the camera in the middle of the day, or you'll be without a phone come the evening for sure.