Those will most likely be between 1400-1550mah , possibly even lower . You're best bet is just to go with a HTC OEM (not knock off) 1500mah battery that can be found in the Touch Pro2, Hero, EVO and a few others.
It's physically impossible to fit a 1800mah cell into the standard slim battery , even the Seidio 1750 is more along the lines of a 1550mah cell . Personally the Seidio is the best slim battery but the HTC1500 is the best bang for your buck , can be had new for under $15 then keep your stock battery as a back up.
If you want an extended battery with the extended cover the best ones are the VZW2100 and by far the best is the Seidio 3500 . I happen to be selling both these $35 for the VZW2150 and $40 for the Seidio 3500