Low MPGs and recent battery issues

Welcome to Prius Chat .

The signs you are talking about are a sign of a weak battery. Those of us that DIY buy the Hybrid Automotive Prolong equipment and maintain the battery.

Your mileage sounds normal for a lot of short trips, so unless you extend your drives, that’s still better than any normal gas only powered car.

You can continue to operate the car just know that the battery is showing signs of age and wear.

 

Good on inflating above the door jamb of 35/33. You will definitely get under inflation wear pattern, assuming the alignment is good. Many here seem to go 42/40, 40/38 or 38/36. Ultimately your choice. Just be sure to NEVER exceed the MAX cold tire PSI rating listed on the tire.

Good. You bought it while it still had the original HV Battery.

I vote normal range for you. Another driver who drives slowly might get better MPG. You would unlikely get into the 40s MPG w/ a Civic/Corolla/Focus.

No surprises here. Colder weather will adversely effect MPG. Add to that short trips, a double whammy.

No surprises here. The car was getting a super workout. The HV Battery was being put to work and the fan came on to keep the battery cool.

Under normal circumstances, I would be concerned, BUT:

1) You had a massive aerodynamic drag sitting on the roof, that only hurts you.
2) Gen2 gas and electric engine is weak. Gen3 gas and electric engines a nice upgrade!
3) The car was fully loaded, and probably exceeded the maximum weight carrying capacity of 810lbs.
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Cause of concern, but no codes/warning lights displayed. Don't second guess the Prius. Crazy well designed.

I vote no need for alarm b/c car likely overloaded and the aerodynamic anchor on the roof only hurts.

See, back to normal.

You could be in early stages of HV Battery failure. People who get HV Battery failure codes have reported frequent, and quick fluctuations on HV Battery SOC (State of Charge): purple to green and hearing the HV battery fan.

Probably. Short trips hurt. The HV Battery is old. Colder temperatures hurt too: moved from SF (never "cold), to an area that gets four seasons and has COLD winters.

If your current residence has an electrical outlet where you park, consider an engine block heater for winter; this will definetely help Winter MPG. Use a timer to come on for maybe an hour before you leave the next morning, and be sure to disconnect the the extension cord going to the block heater.

I vote overloaded car w/ the aerodynamic anchor on the roof was the cause of all the symptoms.

Unlikely the dealership will do a load test on the HV battery. The technician will probably run a "heath check" w/ Techstream, which will report no problems.

You can invest in the Prolong product mentioned in post#2. You should also be setting money aside for future repairs that can be costly. HV Battery replacement is relatively costly at $1600+ for new OEM HV battery or $1600 for new cylindrical module replacement. Many posts about this here. You just need to decide what you will do when faced w/ an HV battery replacement issue and what your plans are w/ the car (short term/long term).

 

I started another thread (look it up under my name) about mpg on short trips. Bottom line, 5-15 is very short and the car will only be returning good mpg after about 10 minutes once it has fully warmed up. So your results are pretty much what I would expect. That said, do check your 12V battery. Mine was in poor shape and putting in a new one made a very large difference in the fuel economy. Also not nearly as expensive as swapping in a new HV battery!

You messed up the car's aerodynamics by putting a box on top and then drove it at high altitudes, both of which are bad for fuel economy. So high 30's is within reason.

It does sound like your HV battery isn't so great. You can get a mini VCI cable and Techstream software and that can show you voltage test points in the battery, if the variance is too large the battery isn't in good shape. The dealer can do the same thing, but the cable will probably cost less than the dealer would charge to run any sort of diagnostic. You might be able to keep a battery like that limping along for a while using a grid charger of some type. If you have not cleaned out the big battery's cooling fan (ever) maybe start with that though. Especially if you have a dog or some other source of fluff to jam it up. Many instructions for doing this, for instance:

 

all the best!