It was VERY USEFUL feature (voltage monitoring). Why every new RB411AH shows 0.0V ?!
Please DO NOT REMOVE THAT FEATURE FROM RB411AH !!!
Documentation and routerboard.com still have informatin: Voltage Monitor Yes
http://routerboard.com/index.php?showProduct=48
Why it does not working on every brand new piece of RB411AH?
Every new RB has new software 
) Use latest RouterOS, if this feature not work write to support@mikrotik.com