First welcome to Pentax Forums.
It may seen logical if a set of rechargeable batteries work in some other device or even digital camera - they ought to work in the Pentax dSLR
- not so.
Pentax dSLRs that use AA's are notoriously battery fussy.
It is an unfortunate fact that is (quite) well known here -
there have been numerous threads about this,
including a sticky in the
Pentax Camera and Field Accessories section that now runs to 14 pages
Sticky: Battery for K-x (and other cameras that take AA's) (
1 2 3 ...
Last Page)
K-x Battery Issue kx battery meter...
So you are not alone.
Fortunately there is a very simple solution.
Short version:
use either -
(non-rechargeable) lithium AA's, like the ones that came with the camera.
or
for rechargeable - use eneloops (or confirmed re-badges) - these are
LSD (low self-discharge) NiMH batteries and as the name suggests have slow self-discharge when compared to regular NiMH rechargeables. BUT the main advantage of eneloops is that they maintain higher operating voltage under load (not just voltage open-circuit/unloaded) - caveat: a good charger should be used from one of the best (read expensive) like the
Maha C9000 (~$51 this is actually a very good/low price!) to a very modestly priced one like the
Soshine SC-C3 (~$14 shipped from Hong Kong)
Longer Version:
Pentax dSLRs use voltage as their level indicator, as well as the threshold for shutdown - operating voltage under load is the critical bit.
Although this was for the K200D - I believe it is applicable for other Pentax dSLRs using AA's.
Please see: Post #
23 in
K200D Battery Meter Problem -
where dmessing measured actual voltage and current draw of his K200D in operation.
For rechargeable - eneloops are known to maintain their operating voltage under load better than any other LSD, please see Post #
57 in
eneloop vs. Kodak Pre-Charged Voltage Maintenance.