1973 Other Dodge Models Battery won't charge

Driving home the other night the volt gauge in the dash of my Coronet was just under halfway and not moving when I applied revs. The indicators stopped working and the dash lights went dim. I managed to get home before the lights went out!
Now, the previous owner recently changed the regulator and alternator for new ones. I did notice that last week when I first started the car the charge would be very high then settle down to where it should be, so I thought nothing of it.
I'm confused!
Could it be a re-occurring problem & thats why the last owner changed those parts or has he missed something & that's why it's happened again!

argh!