So a couple weeks ago I had problems with a connection somewhere in my charging system which caused a severely bouncing voltmeter and eventually the car to stall. Back when I had originally purchased Bonnie she had this issue as well, but I have replaced a number of items and hadn't seen it since.
So I went in and reseated and cleaned all of the main connections and replaced the negative battery cable. I also replaced the 3 small ground connections beneath the ICM. It is running much better, but I notice that if I sit at idle for a few moments the charge (very slowly) starts to trickle down. For example, at start it is always 14+ V on the voltmeter. If I'm driving, it hangs around that range, maybe just 13.75 V worst case. But if I'm at a light or something, you can watch the charge slowly dwindle. It will typically not go below 13 V or so, but it never used to drop like this.
I have had the battery and alternator tested, both passed. Although the guy at Autozone did not recharge the battery before he tested it and it was only at 8 V, so I'm a bit skeptical of that test. The positive cable to alternator/starter was replaced in June. Negative cable was just replaced last week. The negative cable was a cheap crimp-me kind - seen here:
I don't think this would affect the charging system though since the main ground is a single cable. I did notice it is a much smaller diameter than the previous cable. Could this be doing it? A number of places have this cable for my vehicle though.
Grounding bolts to block were soaked in degreaser and cleaned with a wire brush this past week. The alternator connector is a replacement, so I resoldered the connector and taped it up really well. All connections still seem nice and tight. Any suggestions besides reseating everything again?