Originally posted by Jonathan Mac I bought a similar "smart" charger and I believe it is better for the batteries but the K200D has always been dodgy in this respect. I initially bought it thinking the AA batteries would be a plus but they were anything but. I think I spent much more on multiple sets of batteries than I did on the single additional battery I've needed for my K-3.
I just used what I had in my bag. The last set I bought was for my K-50, when I bought a AA tray for it. That was some 2-3 years ago. But I'm not using that anymore since the battery latch broke on the K-50, so that set went to the K200D now (alternating with what's in my AF360FGZII and a spare set).
I think the problem you guys might be having is the mixing of new and old batteries. I only buy sets of 4 rechargeable AAs and the sets are always together. I never mix batteries from one set with batteries from another. So while I do have sets that are newer than others, the fact that they don't mix means they don't stress each other, I think. All of mine still hold a charge pretty well (unless my non-Pentax DLI90, I think I threw out 4 of those already... and one DLI-50)