How long can I run on gas

Personally, if there are no warning lights and the traction battery charges/discharges as expected, you can continue to drive it. I would not drive it if there are steady warning lights and/or the traction battery is not charging/discharging when in operation.

 

How many miles?

What symptoms/warning lights do you have?

Have you had it into a dealership for code check, diagnosis, proposed strategy?

 

The Prius needs a semi-healthy traction battery even when "driven on gas". It starts the engine, for example. It also operates the "transmission". You can't separate the electric part of the hybrid drive train though many try to in their minds.

The answer to your question is "as long as it keeps operating". Not very satisfying I know, but the truth. If the battery has been checked and bad cells were discovered, probably not very long. They get worse fast.

 

until you run out of gas...

 

If you drive it down hills, never run out of it.

 

What leads you to believe the hybrid battery needs to be charged?

 

They said changed Still a good question.

 

Oops!

 

I've been driving mine for over 14K miles since the first Check Your Hybrid System light came on about 9, 10 months ago. Since then had the light come on about 6 or 7 times more as I was careless in watching where the battery level was. So far so good. Took it for a 1000 mile trip a couple of times and seemed to have recharged the battery a bit.
Not that I'm recommending that you do this but my prius has 206K so didn't want to put in $3600 the dealer wanted for a new battery.

 

If you are on the Continental US and a DIY type you could get @2k1Toaster ’s kit of new cells for $1600 delivered with a 2 year warranty. Details in my signature.

 

I'm in Illinois. The car is squeaking and getting old. I'll have to think about spending $1600. I just have to drive in certain way and so far seems good. Thanks though.