Some people are looking for a better battery life, they try to tweak and/or buy a cheap, more mAh battery..
So I checked the Desire HD accessories , a lot of people say, battery's with more than 1500mAh are fake, only Mugen could be a good one.
As for myself, I use a MPBlue 1600mAh and I didn't really measure much difference
Than I saw this topic, http://forum.xda-developers.com/show....php?t=1344761
HTC Evo 3D and Sensation battery, with Mugen 1900mAh, fits in your Desire HD, if you mod your battery cover a bit..
I think it's a nice solution and I will probably try it sometime
checked gsmarena.com and a accesories website, they mention 1750mAh for EVO 3D and 1520mAh for Sensation
but than again, as for the EVO 3D battery, it's 500mAh more, that's about 40% extra battery life, with an original HTC battery