Digital Voltmeter

A dash mounted volt meter will be used to monitor electrical system voltage as you drive. The car battery tends to dampen system voltage swings, generally well within a range of 8 to 16 volts (for the common 12 volt system). So to have the best meter reading you would want a dash mounted volt meter with dial range of 8 to 16 volts, or simply by using digital voltmeter. I've bought this DVM at LYN.net quite reasonable compared to other DVM on the market. It is made from cheap plastic and thin wires; but was neatly designed, compact in size coupled with bright LED reading and most importantly, it works.

Open circuit voltage for a fully charged "12 volt" lead acid battery is actually 12.6 volts (2.1 volts per cell). When viewing the volt meter, a reading less than 12.6 volts would indicate either a somewhat discharged battery or a discharging condition (power being taken out of the battery). A reading greater than 12.6 volts would indicate a charging condition (power being put into the battery). If the battery happens to be significantly discharged, then the volt meter could read a little less than 12 volts even when charging. The main reason why I bought this thing is because my battery indicator was busted (you can see there's no batt light on the cluster). It wasn't a burnt bulb as I've replaced it several times. It is either my alternator internal circuit part is frying to death or the wire connected to the cluster went bad. So this DVM makes me able to sleep well at night knowing the health condition of the alternator is still good.

content derived from http://www.mgaguru.com/mgtech/electric