An ammeter is a volt meter that has essentially been shorted with a shunt, which is just a piece of wire. In our trucks, the shunt is the 12 GA wire that goes between battery and alternator. To get some good info on the dash you could probably design an Arduino circuit to analyze the voltages at the ammeter and display stuff like voltage of the battery and discharge or charge rate. Perhaps even add another wire at the starter to read the amount of current used for starting. An electronics geek would use something like this.
https://www.sparkfun.com/products/12923