I've made a quick search on batteries to try to find the post I read on the K100D and sensitivity to voltage levels (NiMHs of different makes have slightly different voltages), but I haven't found it. I have found these, however:
Battery Life
k100d battery recommendation
K100 has premature 'Low Battery Indication/ shut down"
Which rechargable batteries for K100D?
I do know that the camera was designed to work best with lithium batteries, which is the reason
some, by no means all, NiMHs under-perform.