Originally Posted by LumpyGrits
Volts mean nut'n here. Amps are where it's at.
x2. Volts is nothing more than a measurement of electrical potential. 0 volts is no potential, 600 is a lot of potential.
Amps, or amperes, is the literal amount of electrons passing a point in a given amount of time.
It is certainly possible that the battery has enough amps to operate the radio but not enough to turn the starter.
As suggested, I'd have your battery tested first. If that's good, have the alternator tested.