Desire HD vs. Desire battery?

The normal Desire has a 1400MAh battery.  The HD only has 1230MAh.

At first you'd think that this gives the "old" phone the advantage.  However the HD has a newer type of processor which is claimed to use less battery.  As a result they are supposed to be about the same when it comes to battery life.  I haven't tested them side-by-side yet, so I can't give you a definitive answer on that.

As for which one to buy ... Make sure you go to a shop where they have them both.  The HD looked better in the pictures (at least that's my opinion), but I find that the regular Desire looks better in real-life.  Also the 8mm difference in width just might make the HD too big for some people's hands.  
So be sure to play with it a bit before you buy it.  It would be a shame if you bought one and then found out it's too big to use as your main phone.

From what I read, calibration doesn't seem to help with the HD.  As for the normal Desire, I calibrated mine at the end of the second charge.  So I first did the "pre-use" charge, then set up the phone and depleted the battery, then did a full charge which ended with calibration.  But as long as you do it in the first few days it should do the trick.

Using a non-calibrated battery won't mess it up.  Calibration simply allows the phone to get more out of a single charge.

No idea really, this isn't a HD forum.  We only really deal with the regular Desire.  The LED staying orange is a very occasional glitch on that one tho, so it could be the same for yours. 

I will only do this once:

http://www.htcdesireforum.com/htc-desire-how-to/calibrate-desire-battery-it-worked-for-me-!!/

Next time, search the forum, ok?