It's up. When the rental generator showed up, everything magically appeared as normal. No program errors, nothing wrong except an ethernet fault. I have a BIG disadvantage in not being there to see it, but apparently there was a problem setting the ethernet address, as in, it would return an address of "0.0.0.0". On getting power back on, the normal address magically appeared. I think it has to do with how the PLC5 and the sidecar module share the program info, but no idea.
According to my boss, it acted like there was an EPROM in it when power was restored, but didn't do that before. Confusing. The DC power is totally separate from the mains, it really doesn't make any sense. It might have been a low voltage problem, using the dead batteries as power. Might not have gotten enough DC + to the PLC. I'm thinking in the 20 V and under range.
Weird. Oh, and no one apparently told the bosses the generator was toast for about 4 hours - we did, apparently. It won't be pretty today at their safety meeting.