Trying to figure out if I need a battery or alternator. Now I took the advice from the forum and changed both battery terminals and it was a heck of a job, got a refurbished battery AGM 1 year old , then after about 2 weeks battery light comes on after driving, shut engine off re-start engine light off, turn on radio still fine. Next day which is today Sunday no light, drive to store about 3 miles light comes on. Run the "test" it shows these. Sure can use some more of the great advise from this forum you guys have not let me down at all. Thanks

Re-start after light came on

While driving

At a stop light engine still running

Continue driving now the volts are lower than first 2 .

 

Have you read the check engine codes? There are alternator specific codes that might pinpoint the problem.

From Thermo's description here.
Alternator Check

You want to check the 4 pin connector at the alternator.
Pin 2 (power from fuse box to power the regulator/field), Green/red wire. Should be at the same voltage as you see across the battery. If you have more than a 0.2 VDC difference, you have an issue with the wire or the fuse itself.
Pin 3 (Field control), orange/green wire. This will fluctuate to maintain the output of the alternator at the desired voltage. As long as this voltage is not 0 VDC or battery voltage (12 ish volts), then it is good.

 

I was able to diagnose a similar alternator problem by measureing the current from the alternaror to the fuse box and from the alternator to the battery. See my threaed on AGM battery.
Use a DC clip on meter. Fairly cheap at Harbor Freight.