For charging 7v NiCd from 4.8v:

We came up with a simple circuit to use the cheap DC/DC boost regulators to boost 4.8v solar panels to 7 volts for our NiCd charging.

http://aprs.org/psat/Cubesat-solar-boost-charger-bob-a.doc

You cannot just use the DC/DC boost regulator directly because it has a peak-starting-current which cannot be met with a solar panel. So we added a transistor load switch to hold off the load until after the regulator was started… Works like a champ at near 80% efficiency.

I’m sure there are lots of circuits and parts, but this little circuit more or less worked the first time, so we are going with it.

Bob, WB4APR