Now you have a Voltmeter: Great for monitoring Alt./V-reg operation. But Now how do you monitor battery state while operating car: Charged-Charging-DisCharging?
If the voltmeter is up it is charging. 13.5-14.5 volts is good or you can tell visually with some experience if no numbers (like mine). If voltage is down it is not. I spotted a failing alternator - no charge - by occasional unusual fluctuations in the voltage.
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While monitoring voltage is helpful; it's still only an Indirect means of monitoring state-of-battery.
With a "healthy" battery & an alt. able to handle any system loads; the ammeter typically only sees
a moderate amp load for a relatively short period: (minor recharge after a start)..
