I have (I think) the same transmitter that comes in this kit:
http://www.logitech.com/index.cfm/pr...ONTENTID=10865
(I realize that page doesn't mention bluetooth at all. Neither did the product description when I bought mine. I found mine for pretty cheap though so I took a chance.)

I use it with a pair of Motorolla HT-820 A2DP headphones. I'm quite lucky in that my headphones are expecting a pairing key of '0000' which is exactly what the transmitter sends. I tend to use the transmitter in little bursts of 20-30 minutes, but I haven't been keeping track of how long the battery in it lasts. Still, my gut feeling is that I get at least 4 hours of music out of this thing between charges.

-John