The 14 + volts is ok. Since the voltage is dropping almost 2 volts after the engine is off makes me think you have something draining the battery. That is not that difficult to find, however since the alternator is working, check timming, and get the thing running.

 

The fact that it actually runs, albeit poorly, sounds like the relationship between the spark timing and injector timing is off by a gross margin. It could be the timing chain or distributor gear either of which can jump. Chances are, if the cylinder compression tests show poorly, it's the timing chain, otherwise, the distributor gear.

 

I think that voltage drop is too much... I consider checking all connections thoroughly... check for corrosion on the terminals and and stiff or swollen areas on the battery cables... hooking up the charger is pushing added current and voltage over coming the poor connection...

 

Yes, check the timming. If it is off, set it, and the drive gear is worn it will continue to go out of time. I'd also say if it is the timing chain, you will never get it into time, and yes it will if run, run like crap.