VSC, Master warning light, Battery air vent sucking in air

So of course 3 hours into a 6 hour drive and in the middle of Nowhere, Texas, my VSC, brake system warning light, and master warning light came on. I immediately pulled over and got out the owner's manual, which provided the following helpful advice regarding when the vehicle stability control light comes on: "take your Toyota to a dealership." I was over an hour from civilization in either direction and even farther from any dealerships. I opened the hood just to make sure nothing had exploded and no fluid containers were suddenly empty. Everything seemed the same as how it had looked before I left, but clearly I am not a mechanic by any means.

I decided to drive the 145 miles to get back home and kept my speed under 55 much to the chagrin of everyone else on the road. The battery air intake vent started sucking air at full blast, and turned off after a long while, then turned back on again. The battery symbol on the Info panel also got down to a single bar and stayed that way for over an hour or more, but then it eventually crept back up. About 15 miles from home, I was going downhill and around a curve so I was braking, and I felt the brake give out a little (had not had any brake issues before that). I freaked out and pulled over to let people pass me, and when I put my foot on the gas to accelerate and get back on the road, the engine revved but the car did not accelerate. I tried again and the same thing happened, so I pulled over and got my car towed the rest of the way back to the house. It was dark and I was on some country roads, so I didn't want to risk getting squished like a bug by all the trucks that want to go 90 mph at night. I also noticed when the car was brought to my driveway that a headlight was out, which must've just happened that day. Not sure if that's related to my other problems though.

I started up the car in diagnostic mode, and the 12 volt battery was reading at 12.6 volts. When I turned on the engine, it went up to 14.4 volts as it should. I checked the connections on the 12 volt battery and the negative node seemed loose so I fixed that. I used a code reader and got the code P3020, which indicates a weak hybrid battery cell I believe? The battery had been rebuilt by the previous owner (bought this car 11 months ago) so its not like the hybrid battery is 13 years old. The 12 volt battery also was replaced last December. Is the VSC code likely caused by a weak hybrid battery cell? Any ideas as to what's going on here?