Should it be 13.7 or 14.7 volts.

Normal operation. The charge voltage changes depending on the load on the battery. Since the 12v is used to power all of the user electronics, the more stuff you have on, the higher the charge rate has to be in order to maintain a proper charge in the system. Less demand on the system = lower voltage.

 

Yes it is a standard, the voltage of the accessory battery has to be inside the 12V-15V corridor. The exact voltage depends mostly on the SoC of acc. battery and its recharge needs. The 12V accessory battery in the trunk is used only during the car startup and when the car is ACC mode. During the drive (or READY mode) the 12V bus is ran via DC/DC converter supplied from the main HV battery or precisely from the HV subsystems.

 

so if you put in subwoofer that is connected to the 12v battery and installed a on off switch it would help with the life off the battery as to not use any power when the car is not in ready mode?

 

Uh, guys, a 14.6V reading is NOT "normal"! There is something very wrong.

Check that the battery terminals are secure. Check the ground connection to the body. All this under the hatch floor, right side of the car.

The Prius 12V system will stay in the 13.7 to 14.1 volt range ALL the time when the car is in "ready". You will only see it depart from 13.8V when you have discharged it too much or when the battery is in trouble (about to die).

It's a "float battery", and as such, the voltage shouldn't vary much. It is NOT a "starter battery" delivering very large amounts of current to turn over an engine.

 

14.7 is a little high. I would expect to see that with a smart charger during some charging phases, but not on a Prius.

Tom

 

I have seen several Gen II owners saying that 14.7 is high. I have seen 14.6 to 14.7 quite often on my Gen III from day one. No problem with my 12V battery to date.

Apparently the Gen III runs higher than the Gen II.

 

I am also seeing 14.6-7 on mine while in Ready. But I have been monitoring only about a month, after the winter series of dead battery threads began, and after putting a DMM on the cold battery and discovering that it was 12.1-2, which would be low on previous cars. Unfortunately I didn't watch this when the car was younger (now 2.5 years old) and the weather warmer, so don't recall if this is a change.

The battery in my old car is about 7 years old, running 12.2-5 volts cold, and 13.7-9 when the car is running. Preventative replacement due to age is being considered, I had to replace one of the holddown hooks last week before it corroded through. It snapped as I attempted to unbolt it.

 

With my old battery (the one that was at 10.0 volts at start up) I'd see 14.6 volts after starting up (Ready mode) and driving.

With my new Optima battery, I've see 12.3 - 12.4 volts at start up and 14.6 volts during operation. However, today I saw 13.6 volts. I typically have the radio on. In my morning commute, seat heaters for 10 minutes, radio, occasional heater use. In my evening commute, radio and maybe the heater.

So, basically, I sometimes see 14.6 volts and sometimes 13.6 volts.

 

14.7 here as well...

 

When I was installing the speedlock override on a volunteer's car last week, his on screen vehicle information shows 15.0V. Mine shows 13.7V when in ready mode. As long as you're under 16V you're OK. Most automotive electronics are made to handle voltages up to 16.5V due to various voltages the alternator puts out. If a rectifier and or regulator malfunctions and the alternators puts out 16+V, automakers don't want to replace everything electronic components in the car just because of a faulty alternator. However, if the output voltage reach above 15V, then yeah, you should get it looked at. Normal voltage should be below 15V.
The higher the voltage, the less current it takes to produce the same wattage. If you see 14.7+V turn on the heated seats on both seats, turn on the fan at full blast, turn on the headlights and high beam, interior lights, wiper at fast. That should get voltage down. If it doesn't, pull out the DC converter and I'll give you mine.

 

14.6 here

 

I have checked my 12V battery voltage from time to time but have never monitored it for any length of time. After reading this thread I monitored it to and from work today, 26 miles each way.

My voltage remained at 14.6-14.7 V both ways. I have seen it drop to 13.6 V at times but not today. Temps were low 40's this morning and low 50's this afternoon.

 

Perhaps Toyota cranked it up a bit to avoid some of the dead battery problems of the Gen II.

Tom

 

i see 14.5 all the time which is not too far from expected since lead acid charging cycles run near 2.4 volts per cell (14.4 total) which is probably why the batteries are doomed to a 5 year life under the best of circumstances

 

My 2010 will be 3 years old this July, 43,000 miles, almost always shows 14.6 - 14.7 volts. I have occasionally seen it around 13.6 but not often. No battery problems to date. If I look at the SG in the morning after sitting all night and press the home button to read the 12 volt battery voltage before starting the car or opening a door (I leave a window down overnight once in a while to check this) it is 12.6. Even on a cross country trip in Dec. where I was driving 12-14 hours a day, it was almost always at 14.6.

 

The Gen3 auxiliary battery has temperature sensor and Gen2 one does not.
The Gen3 controls the 12V charge voltage depending on the temperature and charges more efficient than the Gen2.

Ken@Japan

 

Ken, where would this sensor be located?

 

FYI,
Following description is derived from New Car Feature document.

Code:

(r) Auxiliary Battery Temperature Sensor
(1) The auxiliary battery temperature sensor detects the auxiliary battery 
temperature, and transmits temperature signals to the power management 
control ECU (HV CPU).
(2) Based on the signal from the sensor, in order to maintain the optimal 
charging state appropriate to the auxiliary battery temperature, the power 
management control ECU (HV CPU) regulates the output voltage from the DC-DC 
converter.

Ken@Japan

 

It is on the battery clamp.

Ken@Japan