Have written a post about this in another thread, but I'll rewrite it here.
The ONLY official battery for the DHD from HTC, is the 1230mAH battery. There is no official battery from HTC for the DHD with 1500 or 1600 mAH. Using these batteries will void your guarantee, and if they fit into the DHD battery slot and are marked as either 1500 or 1600 mAH, they are fake relabelled 1230 mAH batteries. Why would HTC only make a 1230 mAH battery for the DHD, if a similar sized battery could do 1500 or 1600 mAH? Please give me an explanation that is reasonable for that? It's people who found out that this hoacks makes money, because people are unhappy with the battery capacity of the DHD (for those who don't use the phone properly, don't condition the battery, or use it very heavily). But I (and many others) don't have any issue with the DHD battery, and with normal usage after the "oh it's a new smart phone" period, I get 2-3 days out of my DHD.
And it's not a problem for these people to do this relabel and selling, as it is hard to prove the information given about the battery was wrong. It is very hard to test the capacity of a battery, and no normal people would be able to do so. It requires pretty high tech lab equipment. If the performance is poor, the seller will just blame you didn't condition the battery correctly, or that something else is faulty, and you can't counter prove that easily. So all I can say is be careful in buying these batteries. I'd say they do more harm than good overall most likely...
However, your experience of the supposed 1500 mAH battery, might be due to better conditioning of the battery, which makes quite a difference.