Battery, MPG issue. Is my battery failing?

It does sound like the high-voltage traction pack is losing performance. Keep an eye out for warning indicator lights in the future. Also listen for the cooling fan in the rear seat side bolster running at high speed.

The decreased tank range is a result of the drastically decreasing fuel economy. The fill-up amounts sound normal. The fuel gauge lacks accuracy and consistency in these cars, and the fuel bladder also changes in volume (mostly based on temperature). My fill-ups are usually between 7 and 8.5 gallons, but it drops into the 6s in very cold weather.

Continue to monitor the signs, but you may want to start researching solutions. It's unfortunate that you're encountering this so soon after purchase.

 

Yeah, sounds like a dying battery. What maintenance have you done since you purchased the Prius?

 

Hi and welcome to PriusChat.

This is not unusual at this stage, but they will come. When? Couldn't say, two weeks, a month, maybe longer.

As an aside, I realise you are new here, and probably new to forum etiquette - so this is not a personal dig, just an "educational opportunity" - but, you have posted this same post in three different forums here, which in forum parlance is called cross-posting. Cross-posting is to be avoided as it makes it hard for yourself, as well as respondents, to keep track of what has been said. Also, some of the more seasoned and knowledgable participants are less likely to respond for these reasons. I have reported the posts to the moderators to have them merged, so all the information is contain in one thread.

Back to the question, some have already covered this, but check on your warranty status, not sure if NH is a CARB state, but I'm thinking not. Even so, if the car has a good service record at a Toyota dealership over its life, you may be able to appeal to Toyota USA for a "goodwill assistance" contribution to a new battery. If you are successful, you could get a new battery for the price of a "rebuilt" (and I use this term very loosely") battery. A new battery is vastly preferable to a "rebuilt".

Anyway, at this stage, as advised by others, get the Mini VCI, and see what it tells you about the battery.

I hope you can get things sorted in a reasonably painless way.

 

and check your 12 volt.

 

The gas tank fill-ups they vary on Gen2 due to flexible gas tank bladder, and the colder it gets, the less you can get in there. 500 miles per tank I never got, you really gotta average 50+ MPG to get 500 miles. Keep in mind short trip driving kills MPG cause MPG is 25 MPG first 5-10 minutes. So if you are going highway getting 500 mi/tank and now driving short trips this explains. I don't think we usually see bad MPG when the HV battery dies, but a few say that. Check the 12v per Bisco. NH was former CARB state so no longer CARB.