solar batery charge regulator ic
hey JJ..
Trickle charge will not be too demanding, but those calculator cells are small - 1.7v I think.. Try to get a few, connect in series and test output voltage in bright and dim light.
Those battery management IC's are pretty complex, sensing the optimal charge rate and battery lifetime for quickest charge. A waste for your application I think. Yes, an adjustable regulator and diode are probably a good idea.
Start with the cells (3x-4x in series =>3.5-6v) and add a big (10uf, 20uf) cap across the terminals.
Next add the LDO adusted to 3.7-3.8, and last, a small diode between the LDO and the + terminal of the battery. All grounds connected. This has added feature of running the radio (or whatever it is) off of sunlight if it is used during daytime!