Battery charging problems

Hey everyone, how's it going?

The battery charge gauge in my dash is always dancing irraticaly, it never goes past the middle mark even when accelerated, but as soon as I come to a stop or red light the needle goes way down, still stays in the normal range, but very low, night driving is even worse because the headlights are always on. The end result is that my battery does not stay charged, if I don't run my car for even 3 or 4 days, it struggle to turn on because of low battery, I took both my battery and altenator to my local AutoZone and had them both tested, both are good. I also found a few different websites on how to test the charging system, and according to the numbers it is charging good, I think it read something like 11.9 volts don't remeber exactly. Is this something common or just me, any assistance would be great.

Thanks

1989 5.0 GT Conv

Thanks everyone for your info, I will check all the connections and perform another test to the charge system just to make sure, I don't remember testing the system at the battery last time. One more thing, for those of you that don't have this problem, does the needle in your dash charge gauge staty still?

Thanks again.

Alright, I did everityhing that I can do, I check all the ground connections to make sure they were clean and even applied some of that electrical grease on the connections, retested my battery and altenator and tested good. didn't see any bad or loose wires. Retested the voltage output and read 14.48 at the battery. However I am still having the same issue with the gauge. Let me make something clear, the needle doesn't jump eratically, it moves smoothly but it usually sits towards the bottom of the gauge. even while driving on the freeway at high RPM tha needle sits below the half mark, and againg, at night with all the lights on, I come to a stop and hit the brakes, the needle almost hits the red mark, not good. What to do???????