you have to crack the OBD if you have the high tech cluster (not the one showing a car, but the one that writes). to do that, add up the last 5 numbers in your VIN and remember the result. in the car, press and hold the right dash button (those 2 little buttons where the gauges are). the display will read "Control check ok", but keep pressing untill the display reads test01. once you see that, for each right button click the number will increase (test02, etc...) when you reach test 19 click on the left button. you will read "Lock
n" press the left button over and over again (it will start increasing from 00, 01, etc...) when the number matches the result of your last 5 VIN number, press the right button to scroll further up untill you reach test 01 again. now your hidden menues are unlocked. for each test number, press the left button to see what's inside the menue... i believe the battery voltage is in menu 8 (maybe i forgot...)
last ps: avoid messing with the last test #, because it resets the OBD and no one knows what the hell will this do... (it's number 21 or 23, i forgot again...)