Recommanded NiMh battery cells for HP82162A

[Neve]

Thank you all for your replies.
Now, I have rebuilt the HP41 battery pack a coupe of days ago.
It was originally delivering 5.8v. Now it shows 4.94v. Even after 10h or so (I guess...) of charging it doesn’t go back up to 5.8v. Is this normal? I guess it would be since the original charger was not designed to charge Ni-Mh batteries. But I just want to make sure.
What are the risks of damaging it if I overcharged? I’m not sure how long I left it charging as I just recently read that 10h was the max time.

On a side note, I also read that the charger is just a transformer. No electronics inside. The electronics inside the pack is what regulates the charging cycle. Do I understand this right?
If this is the case, can it be modified to charge faster and/or more efficiently? If so, how?

I know I may sound a bit confused... And I guess I am. I’m definitely not an EE!

Thank you.