Phil, I do not know what you mean by any of this. Almost no car has a "battery condition gauge" . Originally Alpines offered an Ammeter option. I assume that what you have now. You say the gauge is "intermittent" and also state that the charging system "checks" . How did you "check" the charging system? An Ammeter is your fist check and if it is indicating something intermittent, most likely the charging system- Alternator, Regulator, relay,- is intermittent. Pretty uncommon (but not impossible) to have a simple Ammeter be "intermittent". An Ammeter, when wired in correctly, will tell you if the Battery is charging or discharging, mainly telling you if charging system is working. It requires some interpretation to understand the "condition of the battery " from this.
Installing a Voltmeter, instead of an Ammeter (wiring is different, of course) will tell you different information. It will tell you if the battery has a charge, normally about 12 to 13 volts, even before you turn on any lights or start the car. And once the car is running, it will tell you if the charging circuit is working by showing voltage about 14 to 15 volts. But you wont really know the "condition of the battery" until, for example, you turn off the motor and see if the battery has held the charge and will start the motor.
Some people prefer a Voltmeter because an Ammeter is wired "in series" with all the electrics (except the starter) and if the Ammeter fails "open" you lose all power.
Tom