[asid61]

If you don't use some kind of cutoff, the batteries are liable to explode.
If it's just a trickle charger for smaller cells, you could look into some of the commonly available charging ICs. Some of them come in DIP format, although the ones that need fewer components are limited to 300ma/hr charge. You should use one of the buck-boost chargers or use some kind of voltage regulator such as an LM317 with the charger in boost mode.
It's usually easier and cheaper to just buy a charger and hook it up to some kind of regulator circuit coming from the solar panel.