Best battery type for Nagra PL-P

Sometime ago I had to replace the batteries of my PLP. I did not want to wait for a Nagra replacement and bought 8 D size NiCd cells that I wraped in two thin cylinders - I did not nottice any difference in performance. I think they are 4Ah batteries.
NiCd batteries have a lower internal resistance than equivalent size NiMH - but it should not be important for this application that does not ask for high peak current.
Anyway, the advice from Nagra should be considered - in doubt ask John Quick at Nagra USA : high-end.usa@nagra.com .

You should change the batteries as soon as possible - even when the preamp is working with mains the battery has a filter action. I noticed that my PLP batteries where needing replacement because the sound was becoming less full bodied and clear and I tried to use it out of the mains supply.
BTW, to increase battery life you should discharge them almost fully from time to time, specially the first times you use them. Mine lasted for almost four years.