Very few CBX1000 owners understand the onboard voltmeter. In the most basic terms, it is merely a decoration.

To be fair, it's a bit more useful than that, but not much. First, volts are not the best way to monitor a charging system. Charge is current, not volts. Second, even if they were, the voltmeter does a lousy job of being accurate since it is wired some distance from the battery, with the result a 1-2 volt loss. It is always lagging that much. Third, the CBX's charging system like all of Honda's big bike systems from the mid 1970s does not charge its battery at idle. Certainly you have noticed this. At idle the voltmeter will always read less than 12v, even with a perfect system. At 1700 rpm the voltmeter will read over 12v.

Two faults can be reliably indicated by the voltmeter: worn brushes and a slipping drive clutch. Deeper problems are best troubleshooted.