1966 Ford F100 won't start without a jump?

Battery is only a few months old and holds a charge when i pull it off a trickle charge. I had the alternator tested at o'reilly auto and it also passed on their machine. I replaced some very corroded wires and when the charging system is fully assembled it holds at about 12.2 volts. It being an older system i'm not sure if that is low or if it is spec. I would like to know before i spend the money on a new alternator and have it continue not working. Outside of that i replaced the wires to the battery terminals and from the starter solenoid to the starter for corrosion as well, and the truck runs without issue after the jumper cables are disconnected. Any direction helps.
Thanks!

Added (1). I will have the battery tested today. But doesn't an alternator usually put out 14V? The battery is holding the charge that is being put into it. Even with the engine on it only puts out 12.2V. Thanks again

Added (2). It turned out to be the alternator, after it was replaced the charging system did start putting out 14V again. Although in the process it was running off of the battery but i was able to exchange that with the warranty at no cost. The truck is back on the road again.