FWIW ? I bought a Digital Volt meter that plugs into a Cig. Lighter or Power Point, shows system voltage.. Engine Off, then after starting, shows voltage build up as the Alternator kicks in (or doesn't), as you rev up. Also has Green, Yellow and Red LEDs, to give basic battery & charging system condition.
Made by INNOVA, got it at Auto Zone IIRC. 'bout 15~20 bucks ?
Kinda handy for initial check-outs.... when yer by yer self.
Joe