I have recently bough nimh's from model sport to make saddle packs for my cat 2000.
I found the 3000nihms fitted fine with no issues.
https://www.modelsport.co.uk/enrich-...roducts/389536
But the 5000 nimh's are slightly bigger by a millimetre or so and I had to make some alterations to the battery straps for them to fit.
https://www.modelsport.co.uk/enrich-...roducts/396624
I also bought a battery jig off ebay so if our making side by side sticks or saddle packs I recommend you do the same.