2007 Prius - 12v Battery Issue (Please Confirm Diagnosis)

Weird stuff happening? MPGs dropping? Test The Battery | PriusChat
Any result under 12.4 would be bad

 

Is the battery original to the car, I.e. approx 7 years old? If yes, I would be inclined to change it now anyway

 

1. When you are having trouble with a no-start situation and are wondering whether the 12V battery is at fault, turn on the headlights. If they are dim, that is a very good sign that the battery is near-dead. An even better approach is to use a digital multimeter to check the voltage across the battery. A fully-charged AGM battery should measure 12.9V. A discharged battery will measure 11.5V.
2. There is a big difference between ambient temperature of 70 degrees F. vs. ambient temperature of 20 degrees F. A marginal battery will work OK in warm weather. A battery is a chemical device, and chemical reactions slow down at lower temperatures.
3. A loose connection can cause intermittent results. It is easy enough to find the battery and check both the positive and negative cable tightness. Do not forget the negative cable where it bolts to the body.

 

Hi Ryan,

Your 12V battery is seven years old which is very old for an automobile battery. The most likely reason for the symptoms you have reported is a failing 12V battery. Tell your wife that it will be much less costly for you to replace the battery at a time and place of your choosing, instead of waiting until you are stuck in a snowstorm and the car refuses to start, having to arrange for a tow, emergency service, etc.

 

Yes! A 7~8 year old 12 volt battery is overdue for replacement. Look at it like an oil change: a regular, albeit longer service interval is warranted for regular battery replacement, IF you don't like suprises. Emergency vehicles routinely change batteries bi-yearly, or even yearly. 4~5 years is a decent interval for a private owner.

 

The other issue is that it has been below zero in Wisconsin lately. Right?
Quite a bit different than balmy Florida.

Now is the time. Replace the 12v.

 

I would check for voltage at the jump post with a digital volt meter.

If you have close to 12 volts there at the jump post, I think a battery swap is in order. However, if you don't read anything close to that (ie 0 volts), chances are a fuse is blown.

It is real easy to blow fuses in the Prius when jump starting. It can also be rather expensive at times to repair the damage.

Based on what you just posted, it sounds like the Prius is not going into "Ready Mode". From all of your posts so far you have the symptoms of a weak and dying battery. It is unfortunate that the less than two year old battery is acting this way, but it is obvious that it is not supplying enough power.

Jump starting is not the fix. Nor is repeated charging of the battery. Charging will help, but eventually a new battery is the final fix.

Get a volt meter and check for voltage at the jump post. If it reads somewhere between 9 and 12 volts, then the fuses are good. At that point, get a new battery. If you get no voltage or very low, there is either a bad connection or a blown fuse.

11.7 volts under load at the MFD is a dead/dying battery in most cases with the Prius.

 

FWIW, you can purchase a inexpensive digital volt meter at most "dollar stores", harbor freight, or similar discount stores. You can find them starting around $8.00 to $10.00 You don't have to have the top of the line "Fluke" brand meter. Even the bargain brand meters usually measure fairly close to one another and vary just a small amount.

7 Function Multimeter

Unless you are a full time diagnostic repair person who works exclusively on electronic circuitry daily, the above should work for you.

 

I hope the local Toyota dealer's parts department is still open, it is pretty late in the Central Time Zone.

 

As long as no fuses were blown trying to jump start the new battery should solve the problem.

Too many horror stories here on Prius Chat about "failed jump starting" on the Prius.

Let us know how it all works out. And yes, you do have to move a bunch of stuff to get to the battery. Did ours 13 months ago.

 

Does the Prius become READY or not?

I am not sure what "lights just flash around the gear display" means. Can you take a sharp photo of this and post?

I think it is now time for you to have your car towed to your local Toyota dealer. Sorry that the new 12V battery did not help the problem.

 

When in "Ready Mode" you will see the word "Ready" on the dash and the Prius is in normal operating mode. Also in ready mode the led on the power button will be dark (no color).

The above sounds like it is more than just the battery. The thing that is not normal about your situation is the LED color you mentioned which is green. When the Prius is working properly, green signifies "accessory mode". There would be no indicators lit on the dash, however you would see items on the MFD. In your situation you are seeing both the MFD and the warning lights you mentioned which is not normal for accessory mode. Normally you would have to be in "ignition on" mode to see the warning lights and the color of the LED on the power button would be yellow.

I am really curious to learn if you see voltage at the jump post. Either you have blown some fuses when trying to jump start the Prius or you possibly have a bad brake light switch. I suspect the fuses though.

I have changed the battery before in the Prius and sometimes it takes two tries to get it into "Ready Mode".

You might want to take the time to confirm that the brake lights are working when you step on the brake. If they are, with your foot firmly on the brake press down on the power button and see if the Prius will go into "Ready Mode" then. Sorry to hear you are still having problems after doing the battery swap.