I've been using Energizer 2500 mAH rechargeable with my former K110D and now with the K100D SUPER. They seem to drain quite quickly, but I've read about the K100 being finicky about batteries, so that might explain it.
Decided to give these Sanyoo 2700 mAH rechargeables a try. They had 27 5-star out of 31 reviews on Amazon and I've read some good things about Sanyo on this site. At least their Eneloops. Anyway, they only cost $8.99 shipped off eBay using the Free Shipping up to $10 coupon for June!
Hopefully these will be a cut above the Energizers.
If not, $8.99 won't be a big loss.
What does everyone else use on their K110/K100? Is there AA/CRV battery poll that I missed?