Hybrid battery not charging and P0A0F code appeared

2008 Prius with ~106k miles. A couple weeks ago while sitting in a drive-through the red triangle of death appeared along with an exclamation mark and the VSC light. The car turned itself off, then when I turned it back on all lights disappeared and everything was fine. 12v battery was low so I replaced with an Optima yellow top. I used an OBD-II reader and Dr. Prius which found no codes, even voltage for the cells, and > 50% life left for the hybrid battery. Worked fine for another tank of gas or so, then the lights came back. Checked the inverter coolant tank and there's fluid swirling in there. Did another OBD-II scan and am now seeing a P0A0F error which doesn't make sense given the engine starts. Just tried charging the battery to do the full battery test in Dr. Prius again, but this time when I pinned the throttle and brake together nothing happened and the battery did not begin charging whereas a week ago it did charge as expected.

It seems like the hybrid battery is in fair condition but for some reason it's not charging. At this point I'm stumped and am ready to let someone else investigate. I have ~45% charge remaining and it's two miles to the nearest shop - would I be able to make it there so they can take a look?

edit: Just noticed I put this in the wrong forum. Meant for it to go in Gen II Troubleshooting.

 

Too late to edit the OP, but the reason the hybrid battery wasn't charging was because I missed a step and did not have the vehicle in drive . I was able to charge the battery but am still perplexed at the behavior mentioned above. Should also note that the most recent red triangle came after I had driven it until the fuel gauge reached one bar, so perhaps that played a factor.