Another Check Hybrid System Question

Back in June 2021, I got the check hybrid system warning. Took it to a mechanic and he said it's a failing battery but that my 2013 Prius c with 121,000 miles still fell under the 10 year/150,000 mile California warranty and to take it to a dealership. They had cleared the codes, though, so he said to wait until the warning came back on.

It didn't come back on until this week, about 8 months later. And I drive the care pretty frequently. Not far and not everyday but around town 2 or 3 times a week.

I took it into the dealership today but was told my model is past the warranty, It was 8 year/100,000 mile and not the 10 year/150,000 miles. (Before I paid the $400 diagnostic fee, thank goodness)

So came home and did some online searching. I know about the vent/fan in the back seat. When I bought the car in 2018, the engine was revving after letting off the gas and I read that a dirty fan could cause that. I pulled an almost inch thick layer of I don't want to know off the vent cover.

I looked at the fan again but nothing is on it now. When the warning came on again this week, I was on the freeway and started getting the weird engine revving thing again but it was still switching back and forth from the battery and the engine. And when I got home the battery was fully charged.

Could it be anything else? I want to make sure I know what to ask about when I go back to the mechanic.

Thanks!

 

Thanks, y'all!

The car is definitely not covered under the warranty, @2010moneypit? I called 3 dealerships and emailed the CA helpline.

The online searching I've done does sound like the battery is failing. I read something about possibly a fuse or some other things. I really won't know until I take it in to be checked out.

The original mechanic said it was around $3000 to get a new battery and I'm not sure it's worth it. But I'm also not really in a position to get a new (new or new to me) car.

I read something about replacing the failing cells but again, seems a bit like a crapshoot.