what is the voltage of your 12v battery?

12.1 or 12.2

 

that's a bit low, how are you measuring? if the display, i would throw a dvm on the jump terminal with a cold battery.

 

For consistency of conditions (among users) try taking three measurements as follows.

1. Make sure the car was shut down with all accessories (fan/lights/radio etc) fully off.

2. Make sure the car has been sitting (turned off) for at least 6 hours. Even if you just have it in ready for a few seconds it will affect the results.

3. Initially press the power button just once, with your foot off the brake pedal, to enter "accessory" mode. Then use either the display + headlight trick (or better still the display + six "hidden button" screen taps method) to enter the service menu to display the 12v battery voltage. This is the first (no load) measure.

4. Again with your foot off the brake pedal, press the power button one more time to place the car in "ignition on" mode. Let it sit for about 10 to 20 seconds to stabilize and take a second reading of the voltage. This is the second (battery under mild load) measure of the voltage.

5. Finally, place your foot on the brake pedal and press the power button one more time to put the car in ready mode (where the 12v battery is getting charged from the DC-DC converter). Take the final (under charging conditions) measurement.

My results.

Just measured now: 12.2 volts, 11.9 volts, 14.0 volts.
New battery (4 years ago): 12.3 volts, 12.0 volts, 14.0 volts.

 

Wow, it hardly aged after 4 years!!!

What is the life expectancy?



iPhone ?

 

Well most people would say that my readings are too low and I need a new battery or the wheels will fall off. However those are about the readings I have always got, even on my previous battery, and I've never had a single problem.

My original battery (date code Nov 2004) lasted until 2012, so basically about 7.5 years. It never failed, but I just replaced it when the voltage started falling off fairly significantly (like down to 11.0 or less). The one I replaced it with was a cheap non genuine one, so not sure if it will last the same, but yeah so far so good.

 

uart, have you compared to a direct test at the battery terminals?

 

Yeah, from memory the direct voltmeter test on the battery was pretty close to the service menu displayed voltage. Maybe about 0.1 volt higher but not much different, just as long as they are both measured under the same load condition.

The main difference I notice is whether there's a load on the battery or not when you try to measure it. With the service menu method you are never truly measuring the no load (or open circuit) voltage of the battery, because there is always the display and some ECUs powered up while you're doing it.

Short of completely removing the battery, I find the only way to get a good no load measurement with the Prius is to sneak up on it from downwind. Pop the hood (the jump point is just as good a place as any to measure) then close all the doors and wait quietly for around 5 minutes before measuring. The reason for waiting is because as soon as you open a door (or hatch) some of the ECUs power up in anticipation of you driving, so you have to wait a while and they'll power back down. Then you can get something more akin to a true no load measurement, and I believe mine was about 12.6 volts last time I did it this way.

 

thanks, that makes sense. but i recall others getting vastly different readings. maybe they aren't doing it right, or if the battery is weak, it shows a larger difference. i pop my hood the night before, then measure the cold battery at the jump point.

 

Hi Bisco. Why don't you try measuring it from the service menu (all three measurements exactly as I've outlined above) and let us know what readings you get.

 

can this be done on the gen III?

 

I think so if you have the Multi Function Display. I don't, btw.

 

yes, i have the small gps screen.

 

I recently replaced my 12V battery. About three weeks ago we bought a used 2006 Prius. It has been running great, but I was not sure what the battery voltage was. So, (with no lights, radio, etc. on) I checked the voltage via the MFD and it registered 10.1 volts. I was shocked. At this voltage the battery should be dead, but the car was still starting with no issues. Thinking this was not possible I used my multimeter to check the battery voltage at the battery and got the same result. Clearly the Prius does not need much 12V battery power to start. With the new battery in place the MFD readout is 12.6 volts as it should be.

 

welcome and well done!

 

From the Repair Manual:

 

no way to check it on the diagnostic screen like the gen2?

 

Note the interval between the OP's query (Post#1) and the first response (Post #2)! I'd like to know how the New Member (Post #2) came to find this old thread.

 

12.1, 11.9 and 14.1V

Brand spanking new 45Ah AGM. (Actually a few weeks old). Should I be worried? With fan on mid, headlights and rear-defog ON, it sank to 11.1. My rear-defog has 4 broken wires, so only has 3/4th the currentdraw of a normal window.

All on the MFD. Will try to measure again with a multimeter.

 

i wouldn't worry yet, but i would put a charger on it. 12.1 is weak, should be 13 when new. what kind is it?