The voltmeter was wired directly to the battery for an always-on state while indicating the actual battery voltage. The voltmeter draws less than 2 mA and even if a battery maintainer is not used, it would deplete the battery by less than 1.5 Ah per month.
Wiring of the voltmeter to the battery couldn't be easier. The following photos show how the voltmeter cable was routed.
The voltmeter cable used is Belden 8451, 2-conductor (red-black), 22 gauge (7 x 30 gauge). The outer insulation is black with a nominal diameter of 0.138".
The voltmeter cable coming out the back of the voltmeter was routed between the carpeting and lower edge of the ashtray.
The how-to to fabricate the voltmeter can be found on my Technical Stuff page in the Motorcycles section of my SmugMug site (link below).