I have the x31 and now the x41 from a few weeks ago on woot.
The x31 has been great for me.. excellent sound, great bass (better than the x41, actually) and great isolation. (the wife can't hear the game, which makes her happier lol)
With that said - i feel much more immersion with the x41's than the x31's in an a to b comparison. This is to be expected, as the x31's are stereo, and the x41's are surround.
I happily paid 100.00 for my x31's a couple of years ago, after having used a pair belonging to a friend. half the price is a steal. If you missed out on the x41 but still need something - get these! Don't bother with the wired sets - the wires get tangled, trip you up and are a general nuisance.
**edit - re: batteries - i found the battery life to be acceptable. They tended to last about as long as the controller. I used eneloops in both (i've relegated all my eneloops to things like this after discovering NiZN batts - but thats for another post). with controller vibration on, and the volume turned decently high, i would get about 10 hours of play (split over a few days, obviously) out of each. set up my charging station discretely near the xbox, and when one would die (whichever, first) i got in the habit of replacing both, since they were so well matched.
Guy with batt problems - possible you were leaving these on after game play? I notice they took a while to self-power down...