[davepl]

If I understand the way out factory ammeters work, all they do is compare the reference voltage at the harness to the voltage at the main battery junction. If there's more at the harness, it reads as charging, and if there's more at the battery, that shows up as discharging.

With some debating whether an ammeter or voltmeter is better, I thought to myself "both", but what would be even better than both would be two volt meters!

If you had two, one connected at the alternator or dash harness and one connected at the battery you could read both voltages and you'd be able to know what's happening not only with the battery but also with the alternator and the state of charge and where current is flowing.

Taking it a step further, since no one wants two volt gauges, is a single gauge with two needles.

When both needles are high, all is good
When both needles are low, system is broken
When needles are apart, system is either charging or discharging

Ideally the gauge could present the area between the two needles as a span of color, like green for charging and red for discharging.

I'd buy one... but would anyone else? I think it'd tell you a great deal more about the charging system than our current single-needle gauges.