All the Pentax dSLRs using AA batteries work well with the low self discharge (LSD) batteries like Eneloops.
Have a read of this thread
https://www.pentaxforums.com/forums/camera-studio-accessories/92821-battery-k...-take-aas.html - it covers most of what you need to know including other NiMH batteries etc.
I use the Eneloops in my K200D, the flash and the battery grip with no problems at all. Capacity is not an issue as they are all similar (about 2000mAh) - its their discharge curve thats important. The LSD batteries discharge curve is what gives them a long run time
Hope that helps......
Cheers