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.
I hooked mine to the 12 volt feed used to power the instrument panel... it is switched and works fine.
