When completely charged, a crank radio will usually provide 10-15 hours of radio time. If you are using other specs, the time frame will be little. The best news is that all you have to perform to get the radio up and running again is crank it.
When it comes to the lifespan of crank radio, there is no answer for this but usually 500 to 1000 charges, so unless you have hurricane raving your home weekly, we are willing to bet you have a few years out of your gadget if not decades.