They came out for a service call unrelated to the battery backup (I called because of consitent slow downstream speeds). the service guy replaced the battery backup with a new one and told me it has a new firmware on it that doesn't give the reboots anymore. This happened mid January.

battery is plugged back in. shows up as OK in router settings and proved to be useful for our first power outage already. no rebooting symptoms and stable since the new replacement.

i3812V iNID and i38HG router

Firmware version: 6.3.47-enh.tm

Hardware version: 2700-000679-004

  amigasteve, they initially changed batteries because they couldn't figure out reasons for iNID reboots and red light symptoms. Eventually they decided to just tell customers to disconnect batteries until a new firmware (which was the culprit) comes out. Apparently battery backups with new firmware are now being installed.