I can pretty much confirm that K-x I got in Czech Republic is more picky then my old K100D or generally anything I've ever seen.
However, with proper batteries, it seems to work, so at least for now, I am not putting my serial number to either list.
I do have inteligent charger that I use solely for my NiMH batteries, so they should be in pretty good state. It also tells me how much energy goes into each charge so I would know if some battery would start failing or so.
My experience insofar:
Doesn't work:
- Energizer NiMH 2650 mAh (about 18 months old) - freshly charged, with about 2,6mAh going into each batter, worked for about 30 shots before battery depleted. No magic I was able to perform persuaded K-x to use it afterwards. Works without problems in K100D (and normally gives few hundred shots).
- Conrad (NoName) NiMH 2500 mAh (may be 3 year old). Charged and capacity tested (all withing reasonable range of 2,5 Ah), fails to boot at all. Again, while it's no name, capacity wise it's just fine and works in K100D
Does work:
- Freshly bought precharged Sanyo Eneloop - Gave me around 350 shots before giving up, that with heavy playing around with menus and some movies. And maybe even more importantly then number of shots - batteries were really depleted when they came out of camera. My charger was able to extract something like 20-30mAh from each of them before reaching terminal voltage of 0,9V. This means that K-x was able to use all the power that was in the batteries. Besides, I've heard somewhere that Eneloops are not precharged to full capacity, so I expect 2nd cycle to be even better.
As a side note, the open circuit voltage of non working Energizer was actually considerably higher then of working (albeit almost depleted) Eneloops, so camera definitely doesn't use open circuit voltage measurement to determine state and type of battery. On the contrary, it seems to test battery under quite heavy load, and older batteries, even with enough energy remaining, just fail this test. It's also the area where Eneloops, at least according to Sanyo claims, are even better then ordinary NiMH batteries - maintaining voltage even under heavy load. So it's not that big suprise that they work.
So my conclusion so far - I am pretty sure that at least some of the battery problems are cause by using old batteries (which just can't maintain voltage under load), or batteries charged with bad chargers (this destroys NiMH incredibly quickly). This, still, may be a problem for some - Pentax claims that camera works with NiMH batteries, and it obviously does only with some. But for me, I'll be quite happy to use Eneloops or similar. This camera is excellent, and 2 sets of Eneloops are still much cheaper then proprietary battery for most other cameras. Besides, I love the posibility to just use Lithiums for longer trips.