The only problem is that the battery door won't fit back on, so you'll need to break the Desire HD's battery door for the WiFi to work. When you put a case on it, nothing is noticeable.
I'll post pictures soon to prove it's worth.
I'm using my 1900mAh Anker bettery in it right now
Here's what needs to be done to Desire HD battery door:
Then after that's been done, put it back on the phone showed here:
Now put on a case (any will do) and now you have an Evo 3D or Sensation battery working in your Desire HD!!
If you want a new battery door, they are only $5.40 so mod away
Here's a link to the replacement door: http://www.ebay.com/itm/OEM-Back-Bat...ht_3765wt_1163