Readynas OS 6 + Eaton network card M3

While you may not like it, a solution I guarantee is to ditch the Network Card M3 and put in a Network Card MS.  I have exactly that configuration, and it works great.  A seller on eBay currently has them for $30, so I bought a spare.  Unless you have a switch that won't handle the max 100Mbps of that card, you don't need Gigabit Ethernet for simple UPS monitoring, anyway.

From what I have read, the M3 with current firmware requires SNMPv3, which is encrypted, though the data sheet shows it supports V1.  I suspect that the ReadyNAS lacks the proper protocol and/or encryption capability for V3 within it's custom NUT instance due to its age.  I do not know if there is an older version of the Network Card M3 firmware that will allow older SNMP or if you simply need to go into the control interface via HTTPS and enable SNMP V1.   That's a question for an Eaton forum.

Netgear has never explained the difference between the "Powerware" and "Powerware (monitored)" selections.  It has always been my ASSUMPTION that the "monitored" version gets it's information from an instance of Eaton IPM running on another device (i.e., from a separate "monitor"), not directly from the UPS.  That may be how it's working for others, or it may be a firmware/setting issue like I discussed above.  With my Network Card MS, the "Powerware" setting works and no separate monitor is required.