Interestingly(?) both my RK05 and RK05J had an assembly of 3, not 4, 2/3rd
AA NiCd cells for retract, completely decayed of course. I replaced them
with 3 discrete tagged NiMh AA cells (plenty of headroom) soldered and
shrinkwrapped. They work fine, lots of retract force. The clip which holds
them is shaped for only 3 cells so it seems as though there were at least 2
variants. I read the circuit diagram and could see that it would make little
difference whether it was NiCd or NiMh (or for that matter 3 or 4 cells). I
think DEC were a bit overgenerous with the trickle current (though IIRC
NiCds were rather leakier back then).
From: tony duell <ard at p850ug1.demon.co.uk>
The DEC RK07 (and I assume RK06) used 8 1/2 AA cells in a pack (like
2 RK05 retract batteries in series). When I replaced those, I used 2 of
the cordless telephone batteries (that have been recommended for
the RK05) in series.
-tony