HV battery is dying... What now?

It could last to the end of the street, or it could last for months. You will find out how long it lasts the moment you are stranded.

The Prius is a full hybrid with not "backup" systems like the traditional starter on Honda IMA models. It relies on the hybrid system for certain things, and it can't be made to be gas-only.

 

The skills of individuals can sometimes be amazing.
So I wouldn't say converting a Hybrid into a gasoline only vehicle would be impossible.
But it's obviously something that doesn't happen very often and a situation not many if any people are looking to create. Most people want a hybrid to be a hybrid.
And I would suspect that if you think a $3000 dollar investment into a new HV battery is too much, any Hybrid to "Standard" conversion would easily approach that amount or more.

Personally?
If you invested around $3000 dollars a few years back, and got 60,000 miles worth of operation?
I might be happy with that return and simply call it a day.

To try to stretch the return, I think your only move is replacement of HV battery. And refurbished comes with risk, and OEM new, is around $3000....so what do you do?

Harsh truth is you own a Prius approaching 300,000 miles.
There's no possible future for it, that probably doesn't come with the risk of significant amounts of resources having to be invested into continuing it's viability.

 

Once the HV battery is dead, there's nothing to start the engine which uses the MG as the starter motor.

 

welcome! there are rebuilt options, but if you like prius, why not put a new battery in, then, when the time comes, swap the battery into a newer prius that needs a battery? a new battery is a major asset.

 

Couple things:

• Others have already hit on this, but the Prius uses the hybrid system to start the internal combustion engine. Converting it to gas only would require extensive reworking of the car's internals, so much so that I am certain you would be better off just replacing the HV battery instead of trying to figure out how to make it gas only.
• Even if you could get it to be gas only, your mileage would suffer big time.
• If you let the battery deteriorate to zero, it will most likely strand you somewhere. Hopefully it gives you enough of a warning that you will be able to limp home, but there is no guarantee with that approach.

I have a couple of pretty high mileage Prii that I really enjoy, and when this day comes for me, I am going to put in a new Toyota battery. The primary reason for that is that $3k is cheaper than a replacement level vehicle.

I typically buy good used cars for $5k-$10k and then drive them into the ground. Finding the point at which a car is no longer "worth it" is tough, but for me it usually comes when my annual repair bill (for irregular maintenance items) exceeds $5k. That's just my two cents. Good luck!