I would use a charge controller/regulator kind of setup to hold a certain voltage level to charge the cell(s) appropriately from the PV panel(s). Just from looking at my MH-C9000 charger which I use to charge my Eneloops (low self-discharge NiMH cells), something around 1.47V per cell (fully charged), or perhaps slightly lower should be good. You won't need to disconnect the "charge" if it's balanced at the right full voltage level. This basically makes it a "float" charger, just maintaining a full charge in the cells without over charging. Perhaps not ideal for your cells (though maybe your project), but it can work reasonably well, and is better than just connecting the PV panel(s) directly.