Crazy error messages on my 2002 screen

First some background. 2002 Prius, 197K miles, replaced hybrid battery at 140K with a remanufactured battery (by the now defunct Re-Involt). A long time ago, I had problems with the torque sensor paddles on my steering rack, which cannot seem to be fixed, so I just removed the steering relay and am just driving with no PS. It isn't as bad as you think.

After the relay was removed, my display panel has typically shown a "POWER STEERING" warning, and has periodically switched over to other screens like the "energy flow" diagram. It's not been a problem, just one of the whimsies of an older car. She's still kicking along, running a little rough, and averaging about 43mph. Which suits me fine.

coming home last night, I got what I think were "main battery" warnings. There was a small image of a battery at the upper right of the screen. The car ran normally, both up and down a small mountain, then it was over. Ran just fine. Parked it, scanned it with my trusty OBD2, nothing. No cods, no pending codes.

Has anyone ever had this happen? What should I be seeing if the battery is really going bad? When I replaced the original, I was seeing the "turtle bumps" on the dashboard, but I saw none of those here. Any help is appreciated.