Own a 1997 F-150, 4.6 L, 4 x 4. I know it's old but it's in very good body shape, has been undercoated for years. I've only had it for a year. This summer it began to not start (intermittently). The dash lights all come on but the starter will not engage. Brought to my local garage, he changed the starter and the ground cable from the battery. Was ok for a few months and now it's beginning to do the same thing.
Brought it back to him, can't find anything. He did say that the battery is a bit weak, the terminals are spotless (I keep them spotless, coat them with white grease).
I measured the voltage with the engine stopped and with it running. Stopped, the voltage is 11.94, running it is 14.87. This clearly shows that the battery is weak.

My question is would this cause the starter to not engage after 4 or 5 turns of the key and then on the 6th try, the starter turns over? I don't want to spend more money ($ 450) the last time and have the same result. If it's possible it's the battery, I'll replace it no problem.

Thanks if someone can help me or even for reading the thread.