12 volt batt not charging??

I've seen this a couple times but always made it home with the Red Triangle and VSC warning. A year ago, I blamed it on the OEM 12 volt battery and eventually replaced it with a Optima Yellow Top. No more problem until today. Day time driving with my Plug-in Supply 10k rechargeable conversion performing normally. City driving raining but normal Western WA conditions.
Ops! Red Triangle and VSC warning. Other systems operating normal.
I knew, from previous experience that the Prius operating systems would continue to work only until I turned it off. I did turn off the Plug-in Supply controller to isolate that system and observed that the OEM traction battery was at a fairly high state of charge and the ICE was still providing the normal amount of assist to the traction battery through normal street and driving conditions.
I should have driven the 20 + miles to get home, even with the Red Triangle warning. I had done that in the past with the old OEM 12v battery. But I needed gas and went to a station and turned off the system ICE out of habit. Dah!.
Sure enough, the system wouldn't go back into Ready but would go from Park to Neutral. Since it was rain hard now, and I was calling my road service, I ask for a Flat Deck Tow home rather than a jump start.
As soon as I got off the tow truck I put my battery charger on the Yellow Top and it only read 11.7 volts. It's still on charge now.

Now I'm wondering why the power conversion system wasn't charging the 12 volt battery or is my 1 year old Optima bad?? Or is there something about my driving conditions/plug-in conversion that is effecting the charge of this battery. I did a 2400 mile road trip to So. Calif and back to WA without any problems. Car has just 98169 miles right now. About 10k miles on the Plug-in Supply conversion.

Comments or suggestions welcome.

Steve

 

The 12 v batt took a full charge and once I had a Prius aware scanner, I cleared the codes set. Sorry I didn't not them but the were of the low numbers and since I had at one time disconnected the battery to to take no-load and current draw readings, there set codes weren't that significant.
One thing I noticed was a significant current draw on the 12 v battery and later I determined that to be the electric defogger heaters in the windshield vents. I now remember having them on before the initial Red Triangle and this was confirmed when I finally was able to clear the codes and saw that this option was still on. (someday I'd like to check just how much current this system draws.)
So, the codes and Red Triangle have been cleared and all systems seem to be normal.

Lessons learned:
Don't leave the windshield electric heaters on too long. (sometime needed when running on the Plug-in Supply conversion due to lack of ICE run time.)

Keep a Prius aware OBDII scanner in car to read or just to clear codes and the Red Triangle. ( My Torque Pro program didn't detect the codes that were set, hmmm! that is strike two against that program!)

Thanks for all the responses to this post and one final note. Keep you road service insurance paid up. It sure beats walking home or trouble shooting in the rain.

Steve