Engine (almost) always running

$900 is a shite price. Highway robbery!

A new OEM HV Battery can be had for $1600+; $900/$1600 * 100% = 56%; you are a little over half way there.

That is the DC-DC converter recharging the 12V AGM battery. Think alternator from a conventional gas powered car; when gas engine is running, the alternator is spinning producing 13+ volts. When the Prius is READY, the DC-DC converter is producing 13+volts to recharge the 12V AGM battery.

 

Interesting. Had not heard it that way.

I've always done:

1) Let car sit overnight.
2) Foot off break, press Start twice: IG-ON mode.
3) Headlights on HIGH
4) Vent fan on high, AC off
5) Radio on, low volume.
What reading do you get?

Reference the SOC (State of Charge).
​

I imagine readings will be similar: not a fully charged 12V AGM battery.

 

Not much so little its a ridiculous point in this discussion. Been charging using the jump points for about 12 years now. So does everyone else.

 

Those are excellent 12 volt numbers and closely match mine. The 12 volt battery is in good shape. What the hell is a charger transient?

Listen.... do all your battery measurements at the front jump point not the battery.

It does not mater a lick what it measures at the battery it only matters what is measures at the front jump point because that cable on the jump bolt/tang in the fuse box is the main B+ cable from the battery. It supply's 12 volt battery voltage to the main fuse box and the car. 12 volt Power has to go through the bolt on positive post fuse assy on the battery then through a 100 amp fuse in that post assy then down that thick black wire on the way to the jump point before it hits the main fuse box. By checking it at the fuse bx jump point you are checking how its doing across all those components and how well it is doing you can see what voltage the car really see's after going through all those components. Lost of connections before it hits the fuse box. Concerning the 12 volt battery Its the only 12 measurement that counts as far as the car is concerned.

You could have a blown 100 amp fuse in that positive post assy and by measuring at battery only you would never know that fuse is blown.

Been charging my 12 volt battery for years from the jump point it works great. It better!.

What does the sentence in bold mean? Its makes no sense.

 

good idea, we haven't had a minivan in 15 years, might be a nice change

 

Yeah Prius is a little weird compared to to other cars. But stop messing around with the 12 v battery in the trunk nothing good comes from that. You can do everything you need to do from under the hood. Toyota does not want you messing around in the deep dark hatch.

Modern 12 volt battery chargers work great especially the ones with anti sulpahation mode. I like my Ctek MUS 4.3 from amazon. Works really good.

 

OK the reality is, you have a used Prius, that you have no long term familiarity, that is 12 almost 13 model years old. So chronologically, it's an old vehicle for something that is in daily service. Plus it also has "very high miles", so what exactly is VERY high miles? Basically, Older vehicle, driven a lot...means wear and deterioration of possibly everything.

What was the mileage while you were driving on the highway?
Have you hand calculated the mileage as revealed by distance driven between fill up divided into the amount of gas added between fill ups?
On a day to day basis, or moment to moment basis, I wouldn't worry too much about what the system is saying you are getting for MPG. Calculate and keep track of what you are getting by hand, over a longer course of time.

Yes, short trips can kill your MPG...but I would say 34 mpg is disappointing.

Basically however, you have an older Prius, with high miles.
That puts anything and everything as being suspect.
Even though you believe the Hybrid Battery is OK...I would suspect it 1st. If it's the original OEM Hybrid Battery, then it's gone 13 years and....well evidently a lot of miles.
But actually I wouldn't do anything about it...until it throws a code.

In the meantime...you can start jumpiing through all the usual hoops. If the 12 volt is original or just old, changing it is probably a good idea.
Then the usual suspects...tire condition, pressure, oil change..not overfilled?....

I'd start simply...
You say "Recently Bought" ....calculate by hand what your mileage actually is...keep track for a while.
Don't Panic.

 

strangely, that charger is $86. on ctek's website, and $98. on amazon