Check Hybrid System Message

2012 Prius C. Check hybrid system message to pull over comes on while driving 110km/hr on highway along with various warning lights.

Wondering if the check hybrid system message would turn on while driving due to bad 12v battery? As I understand the 12V starts the car so Im not sure why it would cause the gas engine to shut down once started. Waiting for obd reader and the local Toyota joint priced the s34b20L battery at 425$ tax incl (not installed) so I'm a bit hesitant to buy it.

Here is what I did so far since the message came on and car shut down into limp mode:

Restarted vehicle but would not accelerate past 20 and stopped after about 100m. Floor battery fan was obstructed a bit, but clean. Liquids were good. Let it cool to restart but 12V was out of juice and had to boost to start it. Once started gas engine started and ran but turned off after 5s and check hybrid message came on along with various different warning lights than previously (Abs, brake).

Let vehicle sit for a few days, disconnected 12V and reconnected. Started vehicle again (needed boost) and all was normal for a longer time, maybe 15s with gas engine running but then the warning lights and check hybrid system lights came on and the gas engine shut down.

I believe it is still the original 12v. The 12v had to be boosted a few times last Winter on the coldest days. Typically I was only doing very short drives during these times over the course of a few weeks. With that context I didnt think too much of the battery needing a boost when it would go down to -15C. However I am reading a failing 12V can cause a lot of issues.

Should I just get a new battery here? Have I been delaying the inevitable by ignoring warning signs when the battery needed boosts last Winter?