The slight charge says the battery is getting old. On three different stock Mopars, 69 and 70 year the Ammeter would always sit right in the center. On the 70 Roadrunner the Ammeter started showing about 2 needle-widths to the right, the battery was getting weaker, it was about 4 or 5 years old. Replaced the battery and it went back to the center again.
