DS user here too.
SAdly, it's jsut something they do as they age.
When mine was last looked at by a sercie centre they said that it wasnt about battery voltage, so much as current.
I always used to use CRV3's with alkaline AA as my backups.
One day it stopped registering the V3 altogether just as you're describing.
I was suggested to try Eneloop rechargables, as they
apparently can output higher current than other batteries. Not 100% on how accurate that is, but all I know is that they worked.
Discharge rates have been fine with mine, I've not used my DSLR for a while, and the last time I charged the batteries was some time in 2017. So discharge isnt a big issue there.
---------- Post added 18-10-18 at 05:14 PM ----------
Originally posted by Cee Cee Also the firmware version may be relevant to the battery condition determination. ie. parameters may have been amended in later firmware. ... the catch 22 is you need a stable battery supply or external supply for firmware update or it could all end in tears!
Can confirm it's not a firmware issue.
I've got the last firmware on mine, and still it's fussy with batteries.
My theory is that over time some of the components inside degrade and start to draw more power than they did when new, and that some batteries cant supply the current needed.
KInd of annoying, because the DS was the last Pentax DSLR to use off the shelf batteries (without a grip or accessory) wasnt it?
Everything after the DS went to the rechargables (which I dislike, but meh, that's business for ya)