The first generation of Freeplay radios did not use any batteries--only spring and solar power. My Freeplay has a clear case and you can see that there is no battery inside. They later added the rechargable batteries, probably because people wanted to be able to store more than one "spring-full" of energy. I was just looking on their website and it appears that all of their models now include a rechargable battery.

As for durability, the mechanism looks pretty simple and the spring looks quite robust. It's a ribbon of metal about an inch wide. The most delicate part seems to be a single slender rubber belt that connects two gears together. Particularly with the clear case, perhaps UV or just plain age could conceivably make it deteriorate. But considering that the Freeplay company started out making tough, inexpensive radios for remote settlements with no electricity or where disposable batteries are scarce/expensive, I suspect that the band is plenty tough (although what we can buy is not the same model distributed in Africa, at least what was originally distributed).

I don't know of any current hand-cranked radio that doesn't use an integrated rechargable battery. Sometimes, you can find the first generation, spring-powered Freeplay and the portable model on sale. My portable Coleman Outrider (aka Freeplay Ranger) does not use a spring. The hand crank drives an internal generator to charge the battery. The current, full-size Freeplay Plus still retains the spring, which then drives its generator and charges the battery or powers the radio directly.