Do these battery numbers look good?

The better time for more accurate readings is after the car has NOT been run for a number of hours, like overnight. But these numbers show a weak 12V battery. You may get better numbers with a long slow charge. If not, start looking for a replacement.

 

Those are low numbers? 12v supposed to show like 14v or something?

 

Near 14v is the charging voltage (in my case 13.8v in a Gen 2 and 14.4v in a v)
Fully charged would be 12.9v, half charged might be 12.5v
Under 12 is dead.

 

You might try to find an accurate digital VOM and take a reading at the battery itself.
If you're really concerned...
The onboard readout it not accurate.

 

To truly test your battery, you need a battery tester that put a load on your battery and measure the voltage at the same time. If you don't have a tester, then put your car in ACC mode (no READY light) and have someone roll the power windows up and down for you while you measure the voltage. If your battery is healthy, it should read above 12v while the windows are moving.

If your battery is bad, you could try desulfate the battery. I have a battery charger that claims it could do the job. However, I have never use that feature so I don't know if it will work. You may have to take it to a profession to do this. Basically, the battery will need to hook up to a machine that will give the battery strong electrical pulses.

 

I would try a slow charge overnight with a smart charger or a desulfating charger. It may not help much but it's possible. 3 years is at the low end of the typical 3-5 year lifespan for these 12V. And if it doesn't help much you can expect to start experiencing strange electronic symptoms. It is already placing more stress on the system causing less MPG. I think it's just a matter of time. So you have a little time to research battery options.

 

Optima DS46B24R Optima battery direct fit replacement for Prius 2004 + , Prius V & Plug-in Prius with Instructions


Exide AGM Car Battery (Group S46B24R)

 

from toyota service manual

3. INSPECT BATTERY VOLTAGE
Standard voltage:
11 to 14 V
If the voltage is below 11 V, recharge or replace the battery before proceeding to the next step.

 

All the above ONLY makes sense if the battery had been "fully" charged (had enough time to be charged).... for example it takes about an hour driving (or living the car in park) to fully charge a healthy battery after just a few days of unuse ..

I would suggest to use a battery charger .... or leave the car in parked if it is possible safely ... the HV battery will charge the 12V (ICE will come in only if the HV SOC goes low ) even better checking the chargin voltage with an ODBC scanner, the car would keep 14.5-6V when it thinks the 12V is not fully charged and lower it to about 13.5V when it is "done"

 

Your battery is done. Do the test first thing in the morning without starting the car not after long drive. After a long drive your seeing the max rate of what the battery can hold for a charge under load. I don't care about that. I want to see the batteries ability to hold a charge over time. 11.7 is bad after long drive. Should be 12.8.
First thing in the morning yours will be 11.3. Done.

And yes hammering mpg's.

Car is either not driven alot. Or bought used at dealer and sat on there lot for a while possible gone dead. Or it has gone dead with you before and you jumped it.

On Gen II car at about 11.4 it starts throwing an instantaneous red exclamation point on start up. It does not store that code just trying to alert you the battery is bad. Not sure if III does that also.

Replace with Optima asap. Do everything you can not to allow the battery to go dead and leave you stranded and worse at the hands of an AAA tow truck jumpstart.

Avoid the dreaded jump start at all costs. So many Prius's here have incurred $ XXXX. of damage with a bad jumpstart. AS in thousands of dollars not covered under any warranty.

If you can't change the battery out now and you do get stranded and must use jumper cables hook up the jump cables vry carefully via the underhood jump points. Make sure the donor car does not race its engine. Leave it connected till you can see the interior light come on bright. (shut light off during charging and just flash it on once to check that)

Disconnect the cables carefully and say a prayer and then boot the car up.

 

You need to read the batteries with an accurate digital voltmeter.
The onboard display is not accurate.
Didn't your test at auto zone convince you?

 

sounds you are new to prius and prius driving the mpg difference could be or most likely be the driving style .. how about swapping cars with your wife see what can she do with your car ???

 

The 12V battery can't absorb the amount of energy required to cause a drop in fuel economy.
It would be a hot smoking mess back there if it did.
This has been discussed many times on the forums.
I believe you do have a difference in the two cars.
A questionable 12V battery would not cause this problem.
It only boots up the system. Then a DC to DC converter provides the 12V power.
You could use a clamp-on ammeter to see how much current the 12V battery is consuming when it just sits there and 'floats' on the 12V bus. It should be minimal.

Good luck finding the difference!