Shot starter?

12 volts is a dead battery, fully charged it should be at least 12.6

actually the rule of thumb is this

9.6 volts + you can charge it and it may hold a charge, very dead battery
11 volts, about a 50% charge may start car, but only the once
12 volts, about 3/4 charged, most new batteries come this way
12.6 volts, fully charged and good to go
14+ volts, car is running and charging