I use a cheap digital multimeter. the reason why I test the battery is the dash meter show all the way up to the end. i think it is over 16V, and then I use the multimeter to mesure that it is over 17V and some thime it reach 19V I am not sure if my multimeter is correct or not. but, when I use the same multimeter to test the battery in my Altima, show 12.6v (not running) and 14V while you start the engine.

the is the reason why I thought my alternator voltage regulator is gone. But, now Ithink I need to verify this again. thank you all.