Dear all,
Here is my contribution to the forum.
Hope my friends do not hate me because I have modified my HP 41cv.
The point is , I bought it severely corroded by leaking batteries and had nothing to loose.
Therefore I took the risk and did soldering an USB cable directly to the board near the regular charger plugs in.
And voilà: I have experienced that great feeling: it is working again , and updated to modern times.
The positive: becomes independent to N cells and still pretty reversible.
The negative: the extra load of a power bank. But I think it is a small price to pay considering pros and cons.