Yes, I tried that, too. Of course, with these remotes, there is hardly any current draw until a button is pressed. Then I see voltage drop to about 5.5V. Strangely, the pair of batteries that does work in every remote drops further than the ones that don't. Of course, this is a rough measurement with a DVM, I might need to look at it with a scope to see what is really going on.
I also tried hooking the remotes to a USB power supply and they work quite well with 5V or even less.
So the mystery remains, and I am a bit peeved that X10 would ship products like that. These things should work out of the box! Seems to me the were not tested at all.
Thanks,
Pete