I'd suggest to use an after-market monitor with a measurement readout. The idiot light system is just that. I have a Victron and believe it's a good, reliable monitor. The Bogart Trimetric is well regarded, too. If you do go this route, you would probably disconnect any OEM shunt and replace it with the new shunt. It is installed between the (-) phase battery terminal and frame ground.
There are also voltage/amp meters that are less in cost than the Victron/Trimetric but the cost should be considered amortized over the longevity of the battery.
