Do these battery numbers look good?

so this could be something ...

getting interesting

so how did your wife faired with your car ?? low mpg as you ??? (then something to start pointing to the car)

so what was the result when you swapped the batteries ??

also check the tire pressure ... underinflated tire could cause loss of mpg but still not 10mpg

also check the tire make an model if the tire is NOT LRR that alone could explain 10 mpg easily

 

Oh Bill wrong again. So many posts here in the last 5 years of people complaining there HYBRID Battery was discharging over night it turned out they had a very bad 12 volt battery. Apparently when the 12 volt gets really low there is an instantaneous demand of Hybrid battery power upon boot up from the Inverter to charge up this flat battery. This happens very fast faster than the display of the hybrid battery level. Inverter puts heavy load on the hybrid and knocks the hybrid down a few bars. Very fast.

I can assure you a bad 12 volt battery does impair mpg as the Inverter must run much much harder to charge it up constantly as it never reaches what the car thinks is a full charge.

Best way for a pedestrian owner to gauge the health of his 12 volt battery is to hook a battery charger with 2 amp charge mode to the battery using front jump points. In 2 amp mode A healthy battery sitting in a daily driven Prius should show 0 current draw after about 15 minutes.

That's about 13.3 volts for most cheap chargers. If it takes forever to reach zero on the meter or never reaches zero (almost full battery) you know the battery will not charge up fully and is on its way out. This bad battery will also display between 11.4 and 11.9 on the mfd test in load. If the battery is really naughty it will flash an instantaneous red exclamation point on the dash during boot up. Won't log a dtc just flashes. Battery will be around 11.2 for this to happen. It's getting ready to leave you stranded.

Btw, most cheap chargers the meter will show 0 current draw but still only show about 13.3 volts when you check it with a voltmeter. It takes quite a while to reach its full 100% capacity from 13.3 to 13.8. Possibly an hour or more as battery draws very little current from 13.3 to 13.8. so its basically a very slow trickle charge to reach that max 13.8 number.
Even a healthy battery takes forever to hit that 100% mark. And much much longer on a float charger. That is normal. But still should run right up to that 13.3 real quick though on a healthy battery. Most cheap chargers have a red light that will light when battery is full. That takes a long time. But 0 on the meter should be fast.

All this aside if you even suspect your 12 volt is bad just replace it. This will avoid the most expensive lesson you will ever get which is the dreaded bad jumpstart in the middle of the night from a clueless AAA tow truck driver.
Hundreds of reports here about that tragedy resulting in $4000+ in damage to the car. Do everything you can to avoid that.

Minute my 6 year old very well tended oem battery refused to charge up one day out it came.

 

Bill did not say that bad battery has no effect what he said and I agree it doesn't account for the 10MPG hit ... the

"Inverter must run much much harder to charge it up constantly" what exactly this supposed the DC/DC converter will keep the charging voltage 14.5-8V as opposed to 13.5-6V but not significant load (if a cell is shorted then the load is a lot higher but then the battery could not be 11.9 V )

And it is not enough to use the car daily it matters how long car is driven ... it takes approx 30 minutes to put back the charge lost for the boot up !!! so it is quite easy to slowly drain the battery with daily short trips


"This happens very fast faster than the display of the hybrid battery level. Inverter puts heavy load on the hybrid and knocks the hybrid down a few bars. Very fast."

this doesn't make much sense !!! if it is very fast then the current MUST be very high !! the car boots up in what 3-4 seconds so this magic 2 bip loss goes is what 1/3 of the battery capacity discharge at 14 V ... could you please tell us what type of current that may be ... there is a fuse there but what kind of a current the 12V battery can take even for a short period of time ???

The manual says that the chargint current should no more 4.5A ...

 

Edfox,

Of ALL the things you said,, the one thing I can agree with is this:
All this aside if you even suspect your 12 volt is bad just replace it.

This is the expensive shotgun approach, but it works almost every time!

All the rest is ,,,,,