493ah not displaying voltage status with dude

Hi,

I have followed the instructions to have dude display voltage status of mikrotik devices on my network and so far it works ok with 433ah but not working with 493ah or rb750

http://wiki.mikrotik.com/wiki/Display_voltage_for_Mipsbe_devices

from a 433ah device =
oid = 1.3.6.1.4.1.14988.1.1.3.8.0 value = 230

from a 493ah device
oid = 1.3.6.1.4.1.14988.1.1.3.8.0 value = 0

have i missed or omitted something