Got 2x regulated RCR-V3 battery and charger combo, by Mobypower. These are said to be safe for out Pentax DSLRs.
The K100D manual specifically warns against theuse of rechargeable CR-V3 batteries. Not mentioned in the *istD manual, but they weren't available when that was printed. Unless certified by Pentax, I don't think I would want to take the chance.