Why my 2007 Prius 12V battery won't charge

If there was any issue with it charging it would throw many DTC's. If its continually low your probably leaving a light on in the car or a hatch ajar like 233,634 posters have done on this site. Check the car at night arm the alarm.

Most people who have your complaint have one thing in common you do not arm the car alarm every time they get out of the car even in the garage that will alert you too leaving the lights on or a hatch ajar. And they do not own a car charger. Observing its charging behavior on a charger is very informative.

If it was me I would get a volt meter and check the battery when I park it for the night at the FRONT JUMP POINT. Then in the am check the voltage level again. Both done with the CAR OFF. Post them here.

A healthy charged up battery in a G2 Prius should be at around 12.6 volts with the car off.
Those are my observations over 11 years with 3 new battery's.

Ahh the mystery's of the 12 volt battery. The most posted subject on this site.

 

Edit: somehow I missed some of the details in your post....

What do you mean by "2nd pic is in Diagnostic mode"? Do you mean ON, in contrast to READY or ACC?

The 14.2 for the moment in READY is good, but what happened then? Did it drop out of READY on its own? Did you turn it off, and now it won't come READY?

In either case, there are likely to be DTCs to be read, playing to edthefox's point.

If you can get it READY again, it would be interesting to see a voltmeter reading at the battery posts to compare to what the MFD shows at the same moment.

 

Do you have an old laptop that can run Windows, and a J2534 USB dongle that can connect it to the car, compatible with Toyota's Techstream software?

It would be helpful to read the codes that are causing that big red triangle to come on, and if whatever you are using to read codes is telling you there are none, it will help more to use something that can read them.

 

Lots of threads here suggest where to get one for reasonable money. Or if you're in a hurry, it could save time to have a nearby dealer read the codes.

 

Does anyone have an answer to this one ? I have the same issue. Brand new Toyota battery. Drives fine when charged but now acting like it’s dead just a few days later.

is there a fuse on top of the battery or something that prevents it from charging ??

 

yes there is a 100 amp fuse mounted on the top of the battery and also a 5 amp fuse. if the 200 amp fuse was blown the car would not start it would be dead if the other 5 amp fuse was blown it would instantly throw a check engine light.

What year is your car?

Who installed the battery?

Do you own a voltmeter?

Do you arm the alarm every night and also do you look inside the car when parking it for the night to make sure all the interior lights are out?. The package light in the back hatch area sidewall is famous for being left on.

Also there's metal box beside the battery its the back up power supply for the brakes. It is filled with super caps that sometimes go ESR and it starts killing the battery.

Here is a link to the search forums section with "12 volt battery" used as a search term. Start reading:

https://priuschat.com/search/363705443/?q=12+volt+battery&t=post&o=relevance

 

Thank you for the reply. It’s a 2008 with 172k miles that I just bought. I have several of these cars.

I own a multi meter and installed the battery myself. Battery it came with was from 5/21 but was hot. And bowed out on the sides. Napa brand. So I changed it to Toyota. Now several days later it’s dead making me think it’s not charging.

I’m not sure about the box for the brakes. The actuator ? Fuse linkage?

Any help to diagnose why it isn’t charging would be helpful. If it’s a fuse or the inverter I can swap those out but I don’t want to throw random things at it without confirming. Thanks again for the reply, I searched a couple threads but couldn’t find an answer.

fyi car jump starts but dash is dead like the 12v is dead. With a charged battery everything is fine (same thing happened with Napa brand - figured cold weather and bad battery which is why I bought brand new from Toyota)

 

Ok so your dash is dead thats probably why your not seeing any check engine lights or even the red triangle of death.
Its really important you have the dash working if you don't have a OBD code reader capable of harvesting hybrid codes becasue it may have a problem charging the battery because the the inverter may be damaged but you will have no idea its throwing that code unless you can see the dash.

The lcd thats the dash is called the COMBO METER. Very common for it to fail.

Everyone uses Matt@Texas hybrids to buy a new combo meter. There around $100.

Go on you tube and search COMBO METER first video is a guy replacing that dash lcd.

Here's some links:

Combo meter info:

https://priuschat.com/search/364064521/?q=combo+meter&t=post&o=relevance

You need a good obd code reader we all use Dr Prius its a phone app you will need to buy a Clarista off Amazon. Clarista is a Bluetooth obd socket that interfaces with the phone. Dr Prius will pull all hybrid codes and lots of other good stuff. Its a necessity if you own a hubrid.

Here's a Dr Prius info link:

https://priuschat.com/search/364065123/?q=Dr+prius&t=profile_post&o=relevance


Good luck.

 

I found this for matt:

Combination Meters that stop at 299,999 miles, Who's affected and what you can do about it. | PriusChat

 

This is very true.

I don't, so no we all do not use Dr.Prius. While it has its uses and does some useful things, it is not classed as a good code reader. This thread list several options ranging from not much use to very good: Gen2 OBD2 app review. It is stickied at the top of the 'Gen 2 Prius Technical Discussion' forum if you need to find it again.

Again, no it will not. While it will read ECM and some HV (hybrid vehicle) control codes/battery codes (and mixes battery ECU codes with HV Control ECU codes), it by no means pulls all hybrid codes.

Just for accuracy, it's called the combination meter, CM for short. The OP might do better searching using the correct terms.