Thinking about an HP-41CL

[renif]

Your aluminum clip works great. Readout after some 2 h of charging: 2.05 mA (initially up to 5 mA), now slowly decreasing by roughly 0.01 mA/min. Single cell voltage (open circuit) approx. 1.35 V at that point. The charging is signaled with a green LED, which goes out as soon as the cells are full.

Hope that's the information you sought. Anyway, I think a modern replacement is to be set on the calculator budget plan at the end of the year...