Have you tried Sanyo Eneloops?
They usually work a treat in terms of holding the charge and operating the camera longer than standard NiMHs would do. You may want to check out more
K100D tips & tricks.
Regarding the "OK button": Really disappointing that the Pentax rep. couldn't help.
BTW, it is my preferred focus setting. Try it for a while, it decouples focusing from shooting. Many more advanced cameras have a dedicated AF button on the back. I'm glad the K100D gives me the option even though it means I have to give up the "reset AF point to centre position" functionality.