Battery advice for my 2015 Prius IV

Are you calculating your mpg or is this on the dash? What is your tire pressure? I have a Prius II and have never got below 50mpg and typically 53 to 55 per tank. I wonder if your brakes are dragging and you have low tire pressure.

 

Many people here use the Prolong charger from Hybrid Automotive. @jeff652 would know it there are any shops in your area with his equipment. Any reconditioning would not nbe covered under Toyota's warranty. They basically replace filed batteries as determined mainly by vejicle trouble codes. If the check engine light is not on, there are no codes.
I would be surprised if there is an issue with that new a battery that has not been sitting much. The Prius likes to be driven.Without any error codes, any troubleshooting is just guessing.

Is the Hybrid battery fan clean? Hot batteries to not perform as well.

 

Lots of things can cause poor gas mileage.
Please provide the brand and model tires that are on the car.

Please provide the air pressure in each of the 4 tires.

What type of gasoline is in the car? Does it contain any ethanol?

Is air filter relatively clean/new?

What viscosity oil is in the car?

How old is the 12v battery?

Is the throttle body and MAF in need of cleaning?

With the right, relatively inexpensive tools ($50?) you can look at the battery health yourself. But I'd probably focus on the other stuff first.

 

if the battery is not throwing a dash light, then it is operating within parameters, and is not the cause of your poor mpg's.
you probably have a rubbing brake or what all else.

 

Your hybrid battery is under warranty (8 years/100k miles).

Here's a test I've posted before: After you engine is fully warmed up, take a 20-30 mile highway trip using cruise control, and make sure it's round trip. Start the Trip A or Trip B right after you get on the highway. If you're by yourself, you should get slightly over 50 mpg if you set your cruise control at 70 mph. Don't do this when it's too busy to use CC.

If you're tripometer indicates the mpg in the high 30's, then there's something besides the traction battery to check out. At highway speeds, the traction battery doesn't play a large role.

(and as others have asked, it's important to know the tire pressure in each tire)

 

Check tire pressures, brake dragging and possibly wheel bearing failure. I had a rear wheel bearing failure around 70000 miles on my 2014.

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tire pressure. tire type? wheel bearings, brakes, both regular and parking, oil level, air filter, cabin filter, intake manifold, egr, traffic, weather, commute, etc....

 

Spark plugs would be something to check too.

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