Hi Trevor
I’ve got the Pentax *ist DS which takes CRV3 Li-Ion batteries which are 3V batteries.
I purchased a spare set of rechargeable Li-Ion CRV3 batteries from
here – note they are stated as 3.0V.
In some (non-photo) shops, I have seen CRV3 Li-Ion batteries at a stated voltage of 3.3V and 3.6V and I have also read on a newsgroup of the potential to fry your camera if you mistakenly put a 3.6V CRV3 in the camera instead of the 3.0V CR3V.
Why they make CRV3 cells at 3.0V, 3.3V and 3.6V with the same CRV3 designation is beyond me and seems a barbaric practice!
For peace of mind, I would fork out the cash for the Pentax AC Adapter; you’ll sleep easy at nights providing you don’t have to go hungry to buy the mains adapter.
Cheers
Dennis