What should the digital readout be if the battery in a 1986 corvette is charged properly?

Any 12 volt battery in any car should read Just over 12v, closer to 12.5v when charged or closer to 13v while car is running. If the reading is much lower after charge, or goes much higher than 13v while charging, the battery is weak, no good, OR low on acid. (can top up with distilled water!) MY 86 will read 12.3 volts with the car ignition to on but engine not running. It will go to 14 when engine is first run for 1/2 hour or so and drop to 13.5. If you see less than that while the engine is running (ie. 12.3) you could have charging problems.